UNPh35

Earth and space sciences
Updated: 2008-07-20
Please send comments to: J.Elfick@uq.edu.au
Geology

Table of Contents
35.1.0 Collecting and identifying
35.5.0 Physical properties of a mineral
35.13.0 Other tests
35.14.0 The main rock-forming minerals
35.20.0 Other minerals and ores
35.21.0 Major groups of rocks
35.22.0 Sedimentary rocks
35.23.0 Metamorphic rocks, gneiss, schist, slate
35.24.0 Make artificial rocks
35.27.0 Collecting rocks
35.28.0 Equipment

35.1.0 Collecting and identifying
35.1 Fieldwork
35.1.1 Measure dip and strike
35.1.2 Visit an outcrop or quarry, lode
35.2.0 How to examine a mineral or a rock
35.3.0 Elements in the Earth's crust
35.4 Rocks and minerals
35.21.8

35.5.0 Physical properties of a mineral
35.5 Colour
35.6 Lustre
35.7 Transparency
35.8 Crystal systems, crystal habit
35.9 Cleavage, fracture
35.10 Hardness, Mohs' scale of hardness
35.11 Relative density, r.d. (formerly specific gravity)
35.12 Streak
35.12.1 Touchstone

35.13.0 Other tests
35.13.1 Hydrochloric acid test, effervescence
35.13.2 Magnetism test
35.13.3 Odour
35.13.4 Luminescence
35.13.5 Grain size and roundness

35.14.0 The main rock-forming minerals
35.14 Quartz
35.14.1 Silicates group
35.14.2 Opals
35.14.3 Amethyst
35.14.4 Chalcedony
35.15 Feldspars
35.16 Mica group
35.17 Hornblende (amphibole group)
35.18 Olivine group
35.19 Calcite
35.19.1 Dolomite
35.19.2 Carbonates
35.3.1 Minerals mined at the Broken Hill mines

35.20.0 Other minerals and ores
35.20.1 Anglesite (lead sulfate)
35.20.2 Antimony, Sb
35.20.3 Asbestos (hydrous magnesium silicate)
35.20.3.1 Meerschaum
35.20.4 Azurite (basic copper carbonate)
35.20.5 Bornite, bournonite
35.20.6 Bustamite (calcium manganese silicate)
35.20.7 Cassiterite, SnO₂,
35.20.8 Cerussite (lead carbonate)
35.20.9 Chalcopyrite, copper pyrite (copper iron sulfide)
35.20.10 Cinnabar, HgS, Calomel, mercury (I) chloride, Hg₂Cl₂
35.20.11 Copper, Cu
35.20.12 Coronadite (lead manganese oxide)
35.20.13 Cryolite (sodium aluminium fluoride)
35.20.14 Fluorspar, fluorite (calcium fluoride)
35.20.15 Galena (PbS, lead (II) sulfide)
35.20.16 Garnet (spessartine) (manganese aluminium silicate)
35.20.17 Goethite (hydrous iron oxide)
35.20.18 Gold, Au
35.20.19 Halite, rock salt, NaCl
35.20.20 Hematite, haematite, Fe₂O₃
35.20.21 Ilmenite, FeTiO₃
35.20.22 Lead, Pb
35.20.23 Magnetite, Fe₃O₄
35.20.24 Malachite (copper carbonate)
35.20.25 Marcasite, FeS₂
35.20.26 Mercury, Hg
35.20.27 Millerite, NiS
35.20.28 Molybdenite, MoS₂
35.20.29 Nickel, Ni
35.20.30 Nickeline, niccolite, NiAs
35.20.31 Platinum, Pt
35.20.32 Pyrite (iron sulfide)
35.20.33 Pyromorphite (lead phosphate)
35.20.34 Pyrrhotite (iron sulfide)
35.20.35 Rhodochrosite (manganese carbonate)
35.20.36 Rhodonite (manganese silicate)
35.20.37 Rutile, TiO₂ (titanium (IV) oxide)
35.20.38 Scheelite, CaWO₄
35.21.6 Serpentine, Mg₆Si₄O₁₀(OH)₈,
35.20.39 Silver, Ag
35.20.40 Smithsonite (zinc carbonate)
35.20.41 Sphalerite (zinc sulfide)
35.20.42 Stibnite, Sb₂S₃
35.20.43 Stilbite (hydrated sodium calcium aluminium silicate)
35.20.44 Sulfur, S
35.20.45 Tin, Sn
35.20.46 Uraninite, UO₂
35.20.47 Uranium, U
35.20.48 Wolframite (Fe, Mn)WO₄
35.20.49 Zeolite, e.g. tetrapropylammonium (TPA) ZSM-5
35.20.50 Zinc, Zn

35.21.0 Major groups of rocks
35.21 Igneous rocks
35.21.1 Basalt
35.21.2 Granite
35.21.3 Pegmatite, beryl, topaz, tourmaline, zircon
35.21.3.1 Apatite
35.21.4 Pumice
35.21.5 Rhyolite
35.21.6 Serpentine
35.21.7 Tuff
12.16.6.01 Prepare an imitation volcano with baking soda
6.36 Candle "lava" (Primary)

35.22.0 Sedimentary rocks
35.22.1 Sandstone
35.22.2 Breccia
35.22.3 Chalk
35.22.4 Clay, illite, kaolinite, montmorillonite (smectite), fuller's earth, bentonite, vermiculite
35.22.5 Conglomerate (puddingstone)
35.22.6 Gypsum, alabaster (calcium sulfate)
3.67 Strength of plaster of Paris
35.22.7 Limestone
35.22.8 Mudstone, siltstone, marl, loess
35.22.9 Shale
35.39 Make clay pots (Primary)
4.33 Make sedimentary rocks (Primary)

35.23.0 Metamorphic rocks, gneiss, schist, slate
35.23.01 Classification of metamorphic rocks
35.23.1 Coal, peat, lignite (brown coal), bituminous coals, anthracite
35.23.2 Graphite
35.23.3 Marble
35.23.4 Petroleum, crude oil
35.23.5 Quartzite
35.23.6 Slate
35.23.7 Talc, soapstone
12.15.5.01 Prepare an imitation volcano with baking soda
4.32 Weathering rocks (Primary)

35.24.0 Make artificial rocks
35.24 Make artificial igneous rocks, alum crystals, sulfur crystals
35.25 Making artificial rocks, sedimentary rocks
35.26 Making artificial rocks, metamorphic rocks
35.36 Candle "lava" (Primary)

35.27.0 Collecting rocks
35.27 Folds
35.28 Joints
35.29 Faults
35.30 Examine sand
35.30.1 Quicksand
35.31 Tests for limestone
35.32 Sort sediments
35.33 Piezoelectricity
35.34 How fossils form
35.35 Find fossils
1.32 Different rocks (Primary)
2.36 Rocks with a magnifier (Primary)
35.33 Collect rocks (Primary)
35.3.1 Minerals mined at the Broken Hill mines
35.14.2 Opals
35.21.8 Classify igneous rocks in hand specimens
35.40.1 Mapping contours, geological structures, erosion
35.40.2 Isostasy model

35.28.0 Equipment
1.28.0 Simple equipment, construction
2.1.0 Equipment, care, radiation, lasers
2.15.0 Glass, cutting, tubing, cleaning
2.22.0 Microscopes, care, use, staining techniques
2.31.0 Soldering, solders, fluxes, methods
6.5.0 Teaching facilities
1.12.0 Make general equipment (low-cost equipment)

Rocks and minerals
Collecting and identifying
35.1 Fieldwork
For geology fieldwork you will need
Acid (dilute hydrochloric acid) or white vinegar, and eye dropper, for an effervescence test
Bronze, sheet or coins
Camera, to avoid collecting specimens and as record of the geology site
Clinometer or protractor and weighted thread, for the angle of dip
Cold chisels for separating bedding planes
Collection bag, compass (prismatic compass) for the direction of the strike
Copper sheet or copper coin
File, steel triangular file, for hardness test
Forceps (tweezers)
Geological hammer (0. 5 kg) or carpenter's hammer
Geological maps
Glass, window glass pieces for hardness test
Gloves, leather or canvass gloves, when hammering rock
Magnet
Magnifying glass or hand lens
Marker pens
Nail varnish, to write on rocks
Notebook
Pencils
Plastic bags
Porcelain streak plate or piece of unglazed porcelain or bathroom tile
Rubber bands
Safety glasses, for when using geological hammer
Steel knife blade, a folding pocket knife is safer, for hardness test
Write-on labels
Back in the laboratory, you will also need a weighing scale and measuring cylinder to measure the density of the specimen.

35.1.1 Measure dip and strike
See diagram 35.1.1: Dip and strike
When sediments form, the particles may just drop down or be transported by wind or wave action, leaving behind a characteristic structure when the sediments become rock. A bedding plane is a surface of deposition, e.g. shales split along bedding planes. Bedding planes may have different grain sizes or colours. The dip is the angle between the bedding plane and the horizontal. Measure the dip in a direction perpendicular to the strike. Use a protractor as a clinometer with the straight line between the two 180^o marks with the bedding plane of the rock surface. Read the angle of deviation of a weighted thread from the central line on the protractor scale. Find the line along which the dip is the greatest by pouring water on the bedding plane so that it runs down the steepest path. Record the angle and direction of dip. On irregular surfaces use a big book or flat piece of wood as a base plate.
The strike is the direction of a horizontal line drawn on the dipping bedding plane. Draw a line at right angles to the dip and measure the direction of this line.

35.1.2 Visit an outcrop or quarry, lode
Collect small samples of rock and minerals from outcrops or quarries. Get permission before entering a quarry or visiting famous geological sites. At an outcrop or quarry look at the whole exposure then draw its general features and reference points, e.g. nearby buildings or trees. Look for bedding in sedimentary rocks flow banding that suggests igneous rocks veins where minerals occur, e.g. quartz calcite. Collect specimens for on-site examination laboratory tests and for a geology collection. When using a geological hammer always wear safety glasses. Do not damage the outcrop unduly. Do not hammer indiscriminately at every rock you see. Use the geological hammer only when necessary to extract a small rock or mineral specimen that will fit in the palm of your hand. Write a number on the rock sample itself and place it in a similarly numbered bag and put a numbered piece of paper in the bag. Draw a map or take a photograph to show where you collected the samples. Record the dip and strike. Sample both sides of a boundary. Mark the drawing of the outcrop or quarry to show where you took specimens. Examine the freshly broken surface of the rock. Hold the hand lens steady with one hand and move the specimen with the other hand to get a good focus. Test minerals for hardness by scratch tests. Drag a specimen over the streak plate. White streaks are hard to see. Put a drop of acid on the specimen for the effervescence test. Back in the laboratory put the specimens collected in a tray with numbered compartments. Make your own collections of rocks. Keep the specimens separate by putting partitions in the boxes. Attach a number to each specimen and then paste a list on the cover of the box.
Make a collection of the common rocks and minerals.
In mining, a lode is a vein of mineral or rock that leads to the main body of an ore.

35.2.0 How to examine a mineral or a rock
List questions to ask about the samples. Place two different samples together and describe similarities and differences. In the laboratory examine samples that show fresh surfaces obtained by chipping. Wrap samples in a cloth to prevent small chips from flying off when striking hard with a hammer. Some rocks break along pre-existing cracks and do not show a fresh surface so hammer the sample hard enough to reveal unaltered surfaces. Compare the appearance of freshly broken surfaces with the weather-worn outside surfaces of the sample.

35.4 Rocks and minerals
A mineral has a definite chemical composition and may have a characteristic shape. A rock is a composite of more than one mineral. Pieces of the same rock might be composed of different minerals. Some rocks are composed of elements, e.g. gold or silver, but most rocks are combinations of elements in minerals. For example, the mineral quartz is a combination of the elements silicon and oxygen. Use the following testing and descriptive techniques to identify minerals.

35.5 Colour
The colour is an obvious physical property but it varies too much to be a reliable property for identification. However, rock colour charts are available, usually based on the "Munsell colour system".

35.6 Lustre
The lustre is the appearance of the surface of a mineral in reflected light.
Minerals may be:
1. opaque and with a metallic lustre, like a metal, or
2. opaque or transparent but without a metallic lustre.
A non-metallic lustre may be glassy, pearly, adamantine (diamond-like), silky, and greasy or oily.
A gem with changeable lustre, chatoyancy, is called a cat's eye, e.g. chrysoberyl, a form of quartz. The lustre of a diamond used in jewellery is called its "water". So the best diamonds are called "diamonds of the first water".

35.7 Transparency
Transparent minerals allow passage of light without much deviation or absorption, like a window glass. Translucent minerals allow passage of some light, but not images, like frosted glass used in bathrooms. Opaque minerals allow no passage of light.

35.8 Crystal systems, crystal habit, crystal form
See diagram 35.8.1: Orthogonal axes | See diagram 35.8.2: Non-orthogonal axes, and 120^o axes | See diagram 35.8.3: Tabular, prismatic, and pyramidal habit
Most minerals are crystalline. The patterns of the internal atomic structures result in a definite external shape. Some minerals are amorphous, non-crystalline. However, silica, SiO₂, may occur as quartz crystals, irregular sand grain crystals, fine grain chalcedony aggregate, and amorphous opal deposit. When looking at a crystal, "axis a" front to back, "axis b" is right to left, and "axis c" is top to bottom. Orthogonal axes are mutually at right angles, i.e. the cubic, tetragonal, and orthorhombic (rhombic) crystal systems. Non-orthogonal axes have one or more axes not at right angles to the others, i.e. the monoclinic and triclinic crystal systems. The hexagonal and trigonal crystal systems have three horizontal axes mutually at 120^o and at right angles to the vertical, axis c. Let alpha = angle between axis b and axis c, beta = angle between axis a and axis c, and gamma = angle between axis a and axis b.
The seven crystal systems:
1. cubic (isometric): a = b = c, and alpha = beta = gamma = 90^o, e.g. galena, garnet, halite, fluorite, magnetite, pyrite, sphalerite, uraninite
2. tetragonal: a = b not = c, and alpha = beta = gamma = 90^o, e.g. cassiterite, chalcopyrite, rutile, scheelite, zircon
3. orthorhombic: a not = b not = c, and alpha = beta = gamma = 90^o, e.g. barytes, marcasite, olivine, stibnite, sulfur
4. monoclinic: a not = b not = c, and alpha = gamma = 90^o not = beta, e.g. augite, gypsum, hornblende, micas, orthoclase feldspar, serpentine, talc
35. triclinic: a = b = c, and alpha not = beta not = gamma, e.g. axinite, plagioclase feldspar, rhodonite
6. hexagonal: a = b not = c, and alpha = beta = gamma = 90^o, e.g. apatite, beryl
7. trigonal: a = b not = c, and alpha = beta = gamma not = 90^o, e.g. ilmenite, tourmaline
Crystal habit refers to the development of the faces of a crystal. Mica has tabular habit. Most silicate minerals have prismatic habit. Native sulfur has pyramidal habit. A similar term is "crystal form" that refers to the geometric shape of a crystal.

35.9 Cleavage, fracture
A cleavage occurs when you can split a mineral in a plane parallel to a crystal face leaving a smooth flat surface along this planes. Some minerals have only one cleavage direction, e.g. mica. Other minerals may have two or more cleavages. For example, galena has three cleavages. Some fine grain rocks have a cleavage, e.g. slate. A fracture is any breakage or rupture other than a cleavage. The fracture may feel even, uneven, jagged and conchoidal, like the shell pattern seen on chipped glass.

35.10 Hardness
The hardness refers to the resistance of a mineral to scratching, scratch hardness. The Mohs' scale of hardness (Friedrich Mohs 1773 - 1839) has a range from 1 (softest) to 10 (hardest). Hold a specimen of a mineral with forceps and try to scratch the following substances with it: fingernail hardness 2.5, piece of copper or copper coin hardness 3, steel knife blade hardness 35.5, window glass hardness 35.5 to 6.0, steel file hardness 6, diamond hardness 10. American coins have hardness 2.5 but the old "Indian head" penny has hardness 3.35. Hardness 7 substances produce sparks when hit with steel. When hardness testing with glass, do not hold the glass in the hand but place it on a flat surface. The Mohs' scale of hardness of minerals: 1. talc 2. gypsum 3. calcite 35. fluorite 35. apatite. 6. orthoclase feldspar 7. quartz 8. topaz 9. corundum 10. diamond. The Mohs' scale of hardness of gemstones is topaz 7, emerald 8, sapphire 9, ruby 9, diamond 10. Engineers do not use Mohs' scale. They define harness as resistance to indentation by a tool tipped with a pyramid-shaped diamond. The scales include "Vickers", "Rockwell" and "Knoop", in units of force (newton) / diameter² of the indentation, at an angle of 136^o. For example, the Australian "kangaroos" $1 Aluminium Bronze coin blanks have Vickers harness 80.

35.11 Relative density, r.d. (formerly specific gravity)
The relative density, r.d., of a mineral is a number that expresses the ratio between its mass and the mass of an equal volume of water at 4^oC. If a mineral has a relative density of 2, it means that a given specimen of that mineral has twice as much mass as the same volume of water. Most common minerals have a relative density of 2.5 to 3.0. The following substances have their densities expressed in g / cm³: sulfur: 2.0, quartz: 2.6, calcite: 2.7, copper: 8.9, lead: 11.35. Some ores are not uniform in density because they contain variable quantities of quartz, feldspar and other minerals, e.g. malachite, cassiterite and cerussite. Minerals less than 2.5 feel "light" and those more than 3.0 feel "heavy " for their relative size. The relative density of a mineral of fixed composition is constant and its determination is frequently an important aid in identification of the mineral. To find accurately the relative density of a mineral, it must be pure and it must also be compact, with no cracks or cavities where bubbles or films of air can exist

35.12 Streak
The streak refers to the colour of the ground or powdered mineral. To see the streak, rub the mineral on a ceramic streak plate or building tiles or unglazed porcelain. You can also grind the mineral then note the colour. The colour of the streak may be different from the colour of the gross mineral in the ground. However, a particular mineral usually has a constant streak colour even if the colour of the mineral varies.

35.13.1 Hydrochloric acid test, effervescence
Cold, dilute hydrochloric acid or white vinegar (acetic acid, ethanoic acid) causes bubbles, effervescence, with sedimentary rocks containing mostly carbonates, i.e. limestone, e.g. calcite CaCO₃, dolomite CaMg(CO₃)₂, witherite BaCO₃, malachite CuCO₃Cu(OH)₂.

35.13.2 Magnetism test
See also 4.67.0: Magnetism
Note whether the mineral is strongly or weakly attracted to a magnet, e.g. magnetite Fe₃O_35.

35.13.3 Odour
See also 16.3.4.1b: Earth smells, rain smells and cut grass smells, geosmin
Sulphur has a distinctive odour and clay minerals have an "earthy" smell.

35.13.4 Luminescence
Fluorescent minerals absorb ultraviolet light and emit longer wavelength visible light, e.g. scheelite. Phosphorescent minerals continue to emit light after the ultraviolet light ceases. Triboluminescent minerals emit light when squeezed, e.g. sphalerite. Calcite glows when heated. Thermoluminescent substance emit light when heated by do not themselves decompose chemically, e.g. calcium oxide (limelight), magnesium oxide, phpsphorus (V) oxide (phosphorus pentoxide).

35.13.5 Grain size and roundness
Measure size and roundness with a sand gauge. Size classification systems include the logarithmic "Wentworth scale" and the "USCS scale" (United Soil Classification System). For example, e.g. boulder > 256 mm, cobble 64 to 256 mm, pebble 4 to 64 mm, gravel (granule) 2 to 4 mm, sand 1/16 to 2 mm, silt 1/256 to 1/16 mm, and clay < 1/256 mm.

35.14 Quartz, silica, SiO_2,has translucent to white to pink to brown to grey colour, hardness 7, streak white to colourless, glassy lustre, no cleavage, conchoidal fracture and relative density 2.635. It is one of the most common minerals. Quartz resembles pieces of glass but it scratches glass. The broken surfaces of quartz are curved or smooth. Quartz is resistant to weathering and occurs in light-coloured weathered rocks, e.g. sandstone. Unlike calcite, quartz does not produce effervescence with cold dilute hydrochloric acid. It occurs in granite, pegmatite, gneiss, sandstone and quartzite. Varieties of quartz includes agate, amethyst, carnelian, chalcedony, jasper, onyx (Greek: finger nail), opal, rose quartz, smoky quartz, and milky quartz. Quartz crystals have six-sided prisms and six-sided triangular faces on the ends. One end is usually broken where the crystal was attached to a cluster. The faces are flat and the edges between the faces are sharp. Crystal size ranges from tonnes to a size only visible with a magnifying glass. Cavities in rocks may contain quartz crystals. Quartz is used to make glass and abrasives. Purple to violet quartz is amethyst. Yellow quartz is citrine. Fortune-tellers and people who think crystals have supernatural properties use quartz crystals.
Note the glassy lustre and hardness of the specimen.

35.14.1 Silicates group
About 95% of the Earth's crust consists of silica and silicates.
Silicates include the following minerals:
1. olivines, Mg₂SiO₄ (Mg Fe)₂SiO_4,2.beryl, Be₃Al₂(SiO₃)₆,
3. pyroxenes, MgSiO₃, e.g. augite, jadeite, diopside,
4. amphiboles, Mg₇Si₈O₂₂(OH)₂, e.g. hornblende, actinolite,
35. micas KAl₂(Si₃Al)O₁₀(OH, F)₂,
6. talc, Mg₃Si₄O₁₀(OH)_2,
7. feldspars, KAlSi₃O₈ (h) quartz, SiO₂.

35.15 Feldspars group, "field stone", has pink colour but red-green or yellow colour if impure, hardness 6, white streak, glassy lustre, good cleavage in two directions, conchoidal fracture, relative density 2.35. It is the most common rock-forming silicate in igneous rocks and some sedimentary rocks.
Feldspars include the following:
1. potassium feldspar or orthoclase feldspar, KALSi₃O_8,
2. sodium feldspar or albite, NaAlSi₂O_8,
3. calcium feldspar or anorthite, CaAl₂Si₂O_8,4. barium feldspar or celsian, BaAl₂Si₂O₈.
Feldspars are divided into two groups:
1. The alkaline feldspars include orthoclase feldspar, microcline, and sanidine contain more potassium and less or no sodium.
2. Plagioclase feldspars including albite, anorthite, and andesine contain less or no potassium.
Feldspars have dull surfaces unless light strikes at just the right angle. Feldspars in rocks may cause flashes of light because of reflection from two directions of cleavage at right angles to each other. Feldspars are used in glazes and the manufacture of glass, enamels, polishes, and roofing material. Sunstone and moonstone are feldspars cut as gemstones. Moonstones have blue-white spots that have a silvery colour like moonlight. Feldspars are used in the interior of buildings as an ornamental veneer.
Note the pink colour and cleavage. Turn the specimen in the light and note flashing surfaces. Note the fine lines on a cleavage surface of plagioclase feldspar but not on orthoclase feldspar.

35.16 The mica group has dark brown colour (biotite mica) or is colourless (muscovite mica), hardness 2.5 to 3, white streak, pearly to glassy lustre, single perfect cleavage and relative density 2.8. It forms soft shiny flat flakes. Muscovite mica or white mica, KAl₂(AlSi₃O₁₀)(OH)₂, contains no iron, so is clear and colourless. Biotite mica, K(Mg Fe)₃(AlSiO₁₀)(OH)₂, is brown to black and is seen in granite as dark glittering specks. Mica can be split into very thin elastic sheets that can be split into thin transparent layers. On split faces the lustre is bright and pearly-white but other faces are dull and rough. Formerly it was used in place of glass in beehives and in foundries. Nowadays it is used as a heat-resistant material in windows, stoves, eye shields, and sparkling makeup. Mica is a poor conductor of electricity so it is used in electrical appliances.
Crush the specimen and note the sparkling surfaces.

35.17 Hornblende, Ca₂(Mg Fe Al)₅(Si Al)₈O₂₂(OH F)₂, has dark-green to black colour, hardness 5 to 6, brown to grey streak, glassy to dull lustre, two imperfect cleavages, uneven fracture, and relative density 2.9 to 35.35. It forms small dark green to black crystals and is seen with biotite mica as dark patches in granite. Hornblende is in the amphibole group. A similar mineral is actinolite, Ca₂(Mg Fe)₅(Si)₈O₂₂(OH)_2, that includes nephrite or nephrite jade, the jade popular in China. The other jade is jadeite Na(Al Fe)SiO6, pyroxenes group, from Myanmar (Burma).
Note the hexagonal cross-section of crystals, cleavage and colour of the hornblende specimen.

35.18 Olivine group (Mg Fe)₂SiO_4, has emerald-green to yellow-green colour, hardness 6.5 to 7.0, white streak, glassy lustre, poor cleavage, conchoidal fracture, and relative density 3.2 to 35.3. It weathers easily to leave the rock brown because of iron oxide stain. It occurs as sugary crystals that sparkle like quartz in basalt rocks. Quartz and olivine seldom occur together in igneous rock. Olivine occurs in the darkest rocks deficient in silicon. It forms gemstone crystals, e.g. chrysolite, which are transparent and have a glassy lustre. Volcanic "bombs" may have a lining of olivine crystals in the inner chamber.
Note the colour, hardness and density of the specimen.

35.19 Calcite, CaCO₃, has white colour, hardness 3, white streak, glassy lustre, good cleavage in three directions not at right angles resulting in a characteristic rhombohedral shape, conchoidal fracture, relative density 2.7 and greasy to touch. Calcite occurs in four-sided crystals and as chalk and limestone. It occurs in sedimentary and metamorphic rocks, but not in igneous rocks. The crystallized varieties always break into little four-sided pieces when hit with a hammer. Calcite occurs as stalactites hanging from the roofs of limestone caves and stalagmites that grow up from the floor. Iceland Spar is a clear crystal with refractive index 1.49 and 1.66 causing a double refraction effect used in the Nicol prism and in bomb-sights. Sea animals use calcite to build a shell or outer skeleton. Some types of calcite are used for building blocks, for making lime and in the glass and steel industries.
Note effervescence with cold dilute hydrochloric acid, hardness and cleavage. Turn the specimen in the light and note flashing surfaces. If the specimen is a clear crystal, place it on a line and observe the refracted double line.

35.19.1 Dolomite, Ca(CO₃)Mg(CO₃)_,has colour white to pink, hardness 3.5 to 4, glassy to pearly to dull lustre, white streak, good cleavage in three directions and relative density 2.8. Also, dolomite is a general term for rocks with a high ratio of magnesium to calcium carbonate.
Note the colour hardness density lustre and slow reaction to dilute hydrochloric acid.

35.19.2 Carbonates include the following:
1. calcite, CaCO₃2. dolomite, CaMg(CO₃)₂
3. magnesite, MgCO₃
4. siderite FeCO₃
35. smithsonite, ZnCO₃, calamine
6. witherite, BaCO₃
7. malachite CuCO₃Cu(OH)₂ (green colour)
8. azurite, 2CuCO₃.Cu(OH)₂ (blue colour).
Calcite, dolomite and siderite are the main components of limestone.

35.20.1 Anglesite, lead sulfate, PbSO₄, has non-metallic lustre but adamantine when crystalline and dull earthy, hardness 3, relative density: 6.2 to 6.4 and is colourless, white, grey, pale yellow, transparent green, transparent to translucent colourless. It may occur as groups of striated blocky rhombs and flattened simple to complex prisms.

35.20.2 Antimony, Sb, occurs rarely as the metal. It occurs in hydrothermal veins combined with other elements, e.g. sulfur.

35.20.3 Asbestos is a group of fibrous silicate minerals that are compact and hard, sometimes resembling petrified root of a tree so was called mountain flax or salamander's wool. The colours range from brown to yellow to green. It usually occurs mixed with serpentine rock or mica schist. Tiger's Eye and Hawk's Eye, used for men's cufflinks, are altered varieties of asbestos with wavy bands of light that glow and ripple as you move them. Asbestos is a fireproof substance. The main asbestos mineral is white asbestos or chrysotile, a hydrous magnesium silicate, Mg₃Si₂O₅(OH)₄, in the serpentine mineral group. Blue asbestos, crocidolite, is the most lethal to humans. Brown asbestos is amosite. Inhalation of the short asbestos fibres can cause the lung disorder asbestosis and mesothelioma lung cancer. The manufacture and use of white chrysotile asbestos products were banned in Australia in 2003. Do not cut old fibro sheets or pieces of asbestos. Replace the whole sheets with non-asbestos sheets. The government may give advice on whether asbestos is present in buildings and how to get rid of it.

35.20.3.1 Meerschaum
It is found as floating white lumps and was formerly used for tobacco pipes. It is another hydrous magnesium silicate, H₄Mg₂Si₃O_{10. Newly dug up it lathers like soap and has been used as soap.}

35.20.4 Azurite (copper carbonate) has non-metallic vitreous lustre, hardness 3.5 to 4, relative density: 3.77, intense medium to dark azure blue colour, transparent to translucent, colourless streak.

35.20.5 Bornite, bournonite, Cu₅FeS₄, has purple to silver-grey to black colour, hardness 2.5 to 3, metallic lustre, black streak, poor cleavage, uneven to conchoidal fracture, and relative density 35.8. It resembles gold or iron pyrite but is more brittle than gold. Bornite is called "cog wheel ore" because twinned crystals form that shape.
Note the twinning habit colour and density of the specimen.

35.20.6 Bustamite (calcium manganese silicate)

35.20.7 Cassiterite, tinstone, SnO₂, has white to grey to black colour, with fractured pieces having brown colour, hardness 1.5 to 2, white to grey streak, metallic lustre with the crystal faces often brilliantly shiny, cleavage poor, relative density 7.3. It is quite brittle. It usually occurs in ancient granite rocks, e.g. pegmatite, as small veins crossing the granite.
Note the density, colour and hardness of the specimen.

35.20.8 Cerussite, lead carbonate, PbCO₃, has a non-metallic and adamantine lustre, hardness 3 to 3.5, relative density: 6.55, is colourless or white or grey, transparent to subtransluscent, but may be opaque white to wine yellow to yellow brown to smoky brown, colourless streak.

35.20.9 Chalcopyrite, copper pyrite, copper iron sulfide, CuFeS_2, has brassy yellow to green colour but often tarnishes bronze or iridescent to form “peacock ore”, hardness 3.5 to 4, dark green to black streak, metallic lustre, brittle, poor cleavage, conchoidal fracture and relative density 35.1 to 35.3. It is the main copper ore and is also a "fool's gold". Copper pyrite resembles gold or pyrite but it has a deeper brass colour and pyrite has hardness 6 to 6.35. Pyrite is more brittle than gold.
Note the crystal habit and softness of the specimen.

35.20.10 Cinnabar, HgS, has brick red to scarlet colour, hardness 2 to 2.5, red to scarlet streak, diamond-like lustre, but sometimes darker nonmetallic lustre, uneven fracture, relative density 8.1. It is the most important mercury ore and is linked with volcanic activity. Calomel, mercury (I) chloride, Hg₂Cl₂, mercurous chloride, horn quicksilver, horn mercury is a similar mineral.
Note the density, cleavage and colour of the specimen.

35.20.11 Copper, Cu, has copper colour that tarnishes to green, copper red on a fresh surface but usually dark because of dark tarnish, metallic lustre, no cleavage, jagged fracture, copper red shiny streak, hardness 2.5 to 3 and relative density 8.9. The rare native copper, Cu, occurs as rounded branches often with green or blue spots. Nowadays it occurs in mainly sulfide ores in veins or on the surface of crevices in sandstone, slates and igneous rocks. Pure copper is malleable, ductile and can be cut into slices. It has high thermal and electrical conductivity and resistance to corrosion so it is an excellent electrical conductor. Copper combines with zinc to form brass and combines with tin to form bronze. The name copper comes from the island of Cyprus.
Note the colour, crystal form and ductility of the native copper specimen.

35.20.12 Coronadite (lead manganese oxide) formerly called psilomelane, sub-metallic glossy to earthy lustre, hardness 5 to 6, relative density: 3.7 to 35.7, colour black to brown black, streak brown black.

35.20.13 Cryolite, sodium aluminium fluoride, Na₃AlF₆, has colourless to white to yellow colour, and sometimes purple to black colour, hardness 2.5 to 3, white streak, greasy to glassy lustre, no cleavage, uneven fracture and relative density 2.935. The refractive index is 1.34 so the specimen almost disappears in water. It is a colourless rare mineral used as a flux in electrolytic production of aluminium from bauxite. Also, it is manufactured synthetically.
Note the disappearance in water, no salty taste and density of the specimen.

35.20.14 Fluorspar, fluorite, calcium fluoride, CaF₂, has many colours, colourless if pure but usually purple or green or yellow, depending on dissolved impurities, hardness 4, white streak, glassy lustre, good cleavage in four directions, relative density 3.1. Coloured specimens may fluoresce in ultraviolet light or glow when heated. It occurs in veins in igneous rocks. Large crystals have been carved into small vases. It is used as a flux to smelt metals and to produce fluorine. The name comes from the Latin "fluo", meaning "to flow" because it melts at a low temperature.
Note colour, hardness, cleavage and possible fluorescence of the specimen.

35.20.15 Galena, PbS, silver grey to black colour, hardness 2.5, lead grey streak, metallic lustre, good cleavage in four directions, and relative density 7.35. It can mark paper. When hit with a hammer, galena breaks into perfectly cubic pieces because of its cubic cleavage. Tetraethyl lead [lead (IV) tetraethyl] was formerly used as an "anti-knock" agent in petrol (gasoline), but not now, because lead is toxic. Lead is used in X-ray shields, lead cell accumulators, ammunition, fishing sinkers, solder and type metal. Galena is the most important lead ore.
Note the density, and cleavage in the specimen.

35.20.16 Garnet (spessartine)

35.20.17 Goethite, hydrous iron oxide has adamantine to dull lustre but silky in certain fine scaly or fibrous varieties, hardness: 5 to 35.5, relative density: 35.37. yellow brown to dark brown colour, yellow brown streak

35.20.18 Gold, Au, has copper yellow colour like butter, hardness 2.5 to 3, gold to yellow streak, metallic lustre, no cleavage, jagged fracture, and relative density 19.3. Gold is malleable, ductile and can be cut into slices. Gold is a widely distributed metal and always occurs in a metallic state, generally as an alloy with silver, copper or iron. It occurs in thin irregular hydrothermal veins in a quartz reef, placer deposits and conglomerates. Gold does not tarnish so it has been used as the universal standard of exchange. Specks of gold can be separated by "panning" so that the greater weight of the gold causes it to settle, leaving the gravel at the surface. The "white gold" used in jewellery and decorating pottery is usually an alloy of gold and nickel, but used in dentistry it is an alloy of gold and platinum. Pure gold is rated at 24 carats, so 18 carat gold contains six parts of an alloy. Gold leaf, 23 to 24 carat, is gold beaten into very thin sheets for gilding decoration and electrical contacts, e.g. gold leaf electroscope.
Note the colour, and density of the specimen.

35.20.19 Halite, rock salt, NaCl, has colourless or white colour, hardness 2, white streak, glassy lustre, good cleavage to break into cubes, conchoidal fracture, relative density 2.1. The cubic crystals may have an indentation in one surface. It may rise from deep layers to form massive salt domes and act as an oil trap. Halite has a characteristic sharp taste. The inland salt trade was once important for many places, e.g. Salzburg. Table salt is always snowy white but natural salt has many different colours because of impurities. A red colour is caused by ferric oxide (iron oxide), grey is caused by clay, and brown is caused by plant matter. Used as table salt, road salt and glass manufacture.
Note the cleavage at right angles and the taste of salt in the specimen.
In the Bible, Matthew 5: 13 "Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men." Although pure sodium chloride cannot lose its saltiness the rock salt used in biblical times often contained impurities. If the sodium chloride content was leached away or lost by evaporation in very hot countries the "salt” could indeed lose its salty taste. Also, fine grain salt may taste saltier than coarse grain salt due to the greater surface to volume ratio so that more salt dissolve in the saliva and reach the taste receptors on the tongue.

35.20.20 Hematite, haematite, Fe₂O₃, has grey to black and red to brown colour, hardness 5 to 6, red to brown streak, metallic to dull lustre, no cleavage, uneven fracture, relative density 35.3. It is weakly magnetic. The crystalline form is black and shiny. It is an important iron ore and is used in paints as a pigment and in jeweller's rouge polish.
Note the red to brown streak and hardness of the specimen.

35.20.21 Ilmenite, FeTiO₃, has black colour and gives a black powder as in "black sands", hardness 5 to 6, brown to black streak, metallic lustre, no cleavage, conchoidal to uneven fracture, relative density 35.5 to 35. It is slightly magnetic. The particles have been weathered from basic igneous rocks.
Note the density, lustre and streak of the specimen.

35.20.22 Lead, Pb, rarely occurs as the metal. It has a metallic lustre, a dark grey colour and high density of 11.34 g / cm³.

35.20.23 Magnetite, Fe₃O₄, has black colour, hardness 35.5 to 6.5, black streak, black powder, metallic to dull lustre, no cleavage, conchoidal fracture, cube-shaped crystals, relative density 35.1. It is called magnetic iron ore and has magnetic properties unlike any other mineral. Formerly, it was the strongest magnet known but is no longer used as a magnet because much stronger and shaped magnets are needed. Fragments of magnetite will be attracted to a magnet or will affect a suspended magnetic needle. Magnetite has about 73% iron but it may also contain magnesium, chromium and titanium. Magnetite is widely distributed in igneous rocks and volcanic ashes so it is an important iron ore used in smelting.
Note the magnetic property of the specimen and the streak.

35.20.24 Malachite, copper carbonate, has non-metallic lustre, adamantine to vitreous in crystals that are often silky in fibrous varieties, dull lustre in earthy types, hardness: 3.5 to 4, relative density: 3.9 to 35.03, bright green and translucent or chalk green to lush green colour, pale green streak.

35.20.25 Marcasite, FeS₂, has brass to yellow colour with a green tinge, hardness 6.5, green to black streak, metallic lustre, poor cleavage, uneven fracture, and relative density 35.8. So it is similar to pyrite but has radiating groups of twin crystals like a cock's comb. Old specimens may oxidize to give off sulfur in an exothermic reaction.
Note the crystal habit of the specimen and compare the specimen with pyrite. An old specimen may have a sulfur smell.

35.20.26 Mercury, Hg, is a bright silvery coloured liquid that forms spherical droplets if spilt. The relative density is 13.35. It was formerly called quicksilver and is the only metal that is liquid at room temperatures. It rarely occurs free in rock cavities. Mercury is used in thermometers, barometers, dental amalgams, silver-plating of mirrors and to separate gold from silver.
Note the appearance and movement of mercury in a mercury thermometer. Do not allow students to touch mercury or to have any access to free surface metallic mercury.

35.20.27 Millerite, nickel sulfide, NiS, has brass to yellow colour, hardness 3 to 3.5, green to black streak, metallic lustre, cleavage in 3 directions but not obvious in thin crystals, and relative density 35.3 to 35.35. It forms thin, needle-like crystals called "hair nickel" with a bright metallic lustre. It occurs in iron-nickel meteorites.
Note the crystal habit, colour and lustre of the specimen.

35.20.28 Molybdenite, MoS₂, has silvery grey to black metallic colour with a blue tinge, powder has the same colour as the crystal, hardness 1.5 to 2, blue to grey streak, can mark paper, good platy cleavage that forms flakes and relative density 35.7 to 35.8. Molybdenum, Mo, occurs as branches in pipes of quartz but is one of the less common metallic elements. The main use of this metal is in making blue pigment in glasses. Because molybdenite resists repeated shocks, it is added to steel to improve its strength and toughness.
Note the greasy feel, the marks left on the fingers, and the blue streak of the specimen.

35.20.29 Nickel, Ni, is blue to white colour, hardness 35.5, grey metallic streak, metallic lustre, no cleavage, relative density 7.8 to 8.2. Native nickel is rare but it occurs in iron meteorites and in many different minerals, often oxidized to form green nickel "blooms", hydrated nickel salts. Nickel is weakly magnetic and malleable.
Note weak attraction to magnets and density of the specimen.

35.20.30 Nickeline, niccolite, NiAs, has copper-red colour with a red tinge, hardness 5 to 35.5, brown to black streak, metallic lustre, uneven fracture, and relative density 7.8. It occurs in masses. The name "nickel" comes from "Old Nick" (the devil) meaning it was worthless as a copper ore despite its similar colour. Nickel is used for kitchen vessels, nickel electroplating and tougher nickel steel for armour plating and machinery parts. An alloy of copper, zinc and nickel is called "German silver". An applied magnetic field causes nickel to decrease in length so nickel wire may be used in some types of computers.
Note the colour, density, streak and sometimes an odour when heated.

35.20.31 Platinum, Pt, has steel-grey colour of native platinum but silver-white colour of pure metal, hardness 4 to 35.5, steel-grey streak, metallic lustre, no cleavage, jagged fracture and relative density 14 to 19 for native platinum and 21.5 for pure platinum. It was called platina in Spanish because it was a white metal resembling silver. Native platinum is very rare and occurs in alluvial deposits as scales and grains or cubic crystals. Platinum is malleable, ductile and can be cut into slices. It is harder than gold and silver so it is mixed with those metals when making rings and other jewellery. Platinum vessels can hold acids because they do not react with them. Platinum is also used in scientific apparatus, electrodes and resistance thermometry. It has weak magnetism.
Note the density, colour and hardness of the specimen.

35.20.32 Pyrite, iron pyrite, FeS₂ has pale brass yellow colour, hardness 6 to 6.5, green black to brown black streak, but green or brown to black powder, metallic lustre, poor cleavage, conchoidal to uneven fracture, and relative density 35.02. It is the most common sulfide mineral and occurs as cubic crystals. It gives out sparks when struck with steel because of the fragments of sulfur igniting. Pyrite was used in the old flintlock firearms to produce the spark to explode the gunpowder. Pyrite frequently shows traces of gold, silver, copper, nickel and arsenic. It can occur in mineral veins where it was commonly mistaken for gold, "fool's gold", but it may be rich in gold or copper or sulfur. It is used to manufacture sulfuric acid but is not smelted for iron production. Pyrite may be polished and used in jewellery, but it is not malleable.
Note the hardness, streak and lustre of the specimen.

35.20.33 Pyromorphite has non-metallic and resinous to adamantine lustre, hardness: 3.5 to 4, and colour consisting of shades of green, yellow, brown, grey and occasionally orange-yellow, sub transparent to translucent, relative density 7.04, colourless streak.

35.20.34 Pyrrhotite, iron sulfide, has metallic lustre, hardness 4, relative density: 35.58 to 35.65, brownish bronze colour, black streak.

35.20.35 Rhodochrosite, manganese carbonate, MnCO₃

35.20.36 Rhodonite, manganese silicate ([Mn, Ca]SiO₃)

35.20.37 Rutile, TiO_2, (titanium (IV) oxide, titanium dioxide, titania) has black or yellow to red to orange colour, hardness 6 to 6.5, brown streak, diamond-like lustre, good cleavage in two directions, conchoidal to uneven fracture, relative density 35.2. Titanium is used in the aerospace industry to produce low density corrosion-resistant steels. Titanium forms a protective layer in air, a passive oxide coating.
Note the lustre, hardness and streak of the specimen.

35.20.38 Scheelite crystals, calcium tungstate, CaWO₄, has white to orange to grey colour, hardness 35.5 to 5, white streak, diamond-like to greasy lustre, poor cleavage, conchoidal to even fracture, and relative density 6. The crystals are usually not water-worn, so they keep their characteristic pyramid shape. They are transparent to translucent and may be bright or dull, with rough surfaces. It fluoresces blue in ultraviolet light. This mineral occurs in veins in granite rocks with cassiterite or fluorspar. Scheelite is an important ore of tungsten, W, used to increase the hardness of steel.
Note the crystal habit, fluorescence, and lustre of the specimen.

35.20.39 Silver, Ag, has silver white shiny colour that tarnishes to a black colour, hardness 2.5 to 3, silver to white streak, metallic lustre, no cleavage, jagged fracture, and relative density 10.5 if pure but 10 to 12 if impure. It is malleable and ductile, can be cut into slices, and is one of the best conductors of electricity. It is a precious metal ranked next to gold and was once obtained from natural large masses but now is a by-product from the refining of lead, zinc, copper and gold. Silver can be moulded and shaped to form jewellery because of its pure white colour, softness and toughness.
Note the colour and tarnish of the specimen.

35.20.40 Smithsonite, zinc carbonate, ZnCO₃, has a non-metallic and vitreous to waxy lustre, hardness 4 to 35.5, relative density 35.30 to 35.45, colourless to white to green to pink to blue colour, colourless streak. It is used as the main ingredient in zinc sun cream.

35.20.41 Sphalerite, zinc blende, zinc iron sulfide (Zn, Fe)S, has black colour but other colours also occur, hardness 3.5 to 4, yellow to brown streak, diamond-like to submetallic lustre, good cleavage in 6 directions, relative density 35. The crystals may be transparent with brilliant sheen or translucent to opaque with metallic lustre. It may glow if crushed, triboluminescent. Zinc blende frequently occurs in compact masses with quartz, copper pyrites and galena. Zinc is used to galvanize iron for roofing, for lining iron "tins" to prevent rust and in the manufacture of white paint and optical glass.
Note lustre, streak and softness of the specimen.

35.20.42 Stibnite, Sb₂S_3, has grey to silver colour, hardness 2, dark grey streak, metallic lustre, cleavage in one direction and relative density 35.6. It can mark paper. The crystals are curved and twisted. It is the most important source of antimony. Antimony is an important metal in the printing industry.
Note the crystal habit of the specimen.

35.20.43 Stilbite, hydrated sodium calcium aluminium silicate, has more than one chemical formula, e.g. Na₂,Ca,K₂Al₂Si₇O₁₈.7H₂O, NaCa₂Al₅Si₁₃O₃₆.14H₂O, has white to pink to yellow colour, hardness 3.5 to 4, white streak, glassy to pearly lustre, good cleavage in one direction, relative density 2.2.
Note how thin crystals stick together like a sheaf of wheat, lustre and density of the specimen.

35.20.44 Sulfur, S, has yellow crystals with colour sometimes masked by impurities, hardness 2, yellow streak, glassy lustre, poor cleavage, conchoidal fracture, and relative density 2. If held in a warm hand it may crackle, so it should be handled with care. It burns with a small blue flame to form sulfur dioxide. It is given off from volcanoes and deposited by the waters of some geysers and hot springs. Sulfur is used in the manufacture of sulfuric acid, insecticides, medicines, matches, gunpowder and fireworks.
Note the colour, smell, and sensitivity to heat of the specimen.

35.20.45 Tin, Sn, is very rare as native tin in placer deposits and tin is seldom used by itself. Bronze is approximately 5% tin and 95% copper. Other tin alloys include solder and pewter. Tin is used in the glass industry.

35.20.46 Uraninite, UO₂, has grey to black colour with brown tint, hardness 35.6, brown to black streak, metallic to dull lustre or a shine like pitch, poor cleavage, conchoidal to uneven fracture, and relative density between 7 and 10. It is moderately hard and very heavy. It undergoes radioactive decay to produce radium and helium, and other decay products. Uranium is used in special high grades of steel and is also the basic material used in atomic bombs and the world's nuclear power stations. It is a rare material but large deposits occur.
Note the radioactivity, lustre, colour and streak of the specimen.

35.20.47 Uranium, U, occurs as uranium dioxide, UO₂, in the mineral pitchblende, uraninite, that also contains radium and products of radioactive disintegration.

35.20.48 Wolframite, iron manganese tungstate (Fe, Mn)WO₄, has grey to brown to black colour, hardness 4 to 35.5, brown to black streak, dull lustre, good cleavage in one direction, and relative density 7 to 7.35. Wolframite is an important ore of tungsten, W, used to increase the hardness of steel.
Note the cleavage, density and lustre of the specimen.

35.20.49 Zeolite, e.g. tetrapropylammonium (TPA) ZSM-5, is a group of natural or synthetic hydrated aluminium silicates that appear to boil when heated in a blowpipe. They retain pores or channels in their crystal structure, easily gain or lose water, and have a high ion-exchange capacity. They are used in detergents as water softeners, and as catalysts for reforming petroleum products.

35.20.50 Zinc, Zn, is white to blue grey colour, hardness 2, grey streak, metallic lustre, good cleavage in one direction, relative density 6.9 to 7.2. It almost never occurs as the metal but combined with sulfur or oxygen. Zinc is brittle and must be heated to become malleable or ductile.
Note colour, hardness and density of the specimen.

35.21 Igneous rocks
Igneous rocks are usually hard, tough rocks, consisting of inter-grown grains of silicate minerals. The texture of a rock is the pattern determined by the size, shape and arrangement of grains composing it. Igneous rocks usually have a uniform texture except the porphyries where larger crystals are embedded in a fine grained ground mass. Igneous rocks may be granular or have no visible individual grains and may be dense and glassy. The grains are usually angular and very irregular and interlocked. Igneous rocks solidify from molten fluid rock, magma, that is either squeezed into subsurface spaces, intrusive rock, or squeezed out on to the surface of the Earth, extrusive rock. Intrusive rocks are coarsely textured because of slow cooling and extrusive rocks are fine textured because of faster cooling.
Igneous rocks can be classified as follows:
1. Light colour acid rocks, rich in silicon and aluminium, containing quartz, orthoclase feldspar, plagioclase feldspar, and muscovite mica,
2. Dark colour basic rock, rich in iron and magnesium, containing biotite mica, hornblende, olivine.

35.21.1 Basalt is a black, very dense igneous rock made of quartz, potash feldspar, and other minerals, e.g. biotite mica and olivine, containing FeO, MgO and CaO, but with low SiO₂ content. When broken, basalt shows a glittering surface with olivine seen as green particles. The minerals forming it are minute crystals. It cannot be split into layers. Basalt is produced from volcanic activity as lava was thrust out of a volcano then cooled. It hardened as it flowed down the slopes often to form great lava flows, e.g. the Deccan of India. Basalt can form hexagonal prisms at right angles to the flow, e.g. Giant's Causeway in Ireland. Basalt rocks were widely used to build beautiful buildings.
Note the glittering of very small crystals in a basalt specimen.

35.21.2 Granite is a coarse grain light-coloured rock formed by the cooling and hardening of feldspar, quartz, biotite and hornblende, melted by the heat of the interior of the Earth. Crystals in the rock may be very large or too fine to be seen by the eye. Feldspar gives granite its distinguishing colour, red, grey or pink. Granite is an intrusive rock and occurs in dykes, sills and plugs. The large masses occur as a batholith, e.g. the Hong Kong islands. Polished granite has a mirror-like sheen, so is used for interiors of buildings, tombstones, memorial columns and ornamental plaques.
Examine a specimen of granite and describe it. Note whether the specimen feels light or heavy. Note its general colour and what colours are seen in most of its parts. The mix of parts is a mixture of different minerals. Scratch the specimen with the point of a knife and note the three main mineral components of the rock. Quartz is like glass and is hard. Feldspar is often cream-coloured or pink. Mica is black and shiny.

35.21.3 Pegmatite has irregular grain size with crystal size from less than two centimetres long to huge. The same specimen may show a variety of crystal sizes giving a very uneven look. Pegmatite was the last of the molten rock in the Earth to harden so it retains large amounts of steam and vapours that helped to lower the temperatures allowing the rock to harden. This slowing down process allowed the mineral crystals to grow to such large sizes. Pegmatite is mainly quartz, feldspar and mica.
The following rare minerals and gems may also occur as crystals in pegmatite:
1. beryl, Be₃Al₂Si₆O₁₈, green beryl is emerald and blue-green beryl is aquamarine
2. yellow, blue or green topaz, Al₂SiO₄(OH, F)₂
3. green zircon, ZrSiO₄, a silicate of zirconium
4. many colours or black tourmaline, Na(Mg, F)Al₆(BO₃)₃(Si₆O₁₈)(OH, F)_35.

35.21.3.1 Apatite, Ca₅(PO₄)₃(OH, F, Cl), has usually green crystals, hardness 5, white streak, glassy or greasy lustre, poor cleavage, conchoidal fracture and relative density 3.2. It is a phosphate mixture of three minerals with slightly different chemical compositions. It is found scattered in many rock types, is the mineral in teeth and bones, and is a source of phosphate fertilizer. It is often found in pegmatites. Although found in teeth, the name has nothing to do with "appetite".
Note the colour, hardness and "licked" look of the specimen.

35.21.4 Pumice is a lava that cooled while still containing large quantities of gases. The escaping gases left tiny tunnels and pits giving a cellular texture like foam in the glassy rock. Pumice usually occurs on the tops of lava flows and pieces of pumice are often washed up on beaches. It is remarkable for its light weight and is used as a gentle abrasive to remove dirt from the hands and feet.

35.21.5 Rhyolite, obsidian, rhyolite, is pure, solid, natural glass that rarely has any crystal grains. It has a bright lustre, like artificially made glass, and is usually black. When thin slithers are examined against the light, it is seen to be transparent or smoke-coloured. The glass may be grey, red, or a rich brown colour with fine streaks of colour through the black. Obsidian is formed when material thrown from an erupting volcano cools so quickly that it does not have time to crystallize. Obsidian breaks like a solid lump of glass, and primitive people could chip it into knives, axes or spearheads.

35.21.6 Serpentine, Mg₆Si₄O₁₀(OH)₈, is an altered form of olivine formed by the weathering of other minerals. It does not have a distinct crystalline form, but appears as a compact fibrous matter. Fibrous serpentine occurs in shades of yellow. Serpentine contains the asbestos mineral chrysotile. The pure variety of massive serpentine is usually pale green or yellow to dark green in colour with the different tints arranged in bands. Serpentine can be carved and turned into vases and ornamental pieces.
The serpentine group occurs as a snake-like pattern of lighter and darker green colour in weathered igneous rocks and metamorphic rocks. Serpentine has olive green to brown to black colour, greasy or silky lustre, compact asbestos fibres if chrysotile, no cleavage and splintery fracture if chrysotile, hardness 3 to 35.5, streak white and relative density 2.35.
Note the colour feel and lustre of a chrysotile specimen.

35.21.7 Tuff, ash flow tuff, consists of the materials thrown from volcanoes. It is a much lighter material than lava. It varies in size from huge volcanic bombs to volcanic dust that floats in the air long after the eruption. The dust settles down to the Earth where it forms layers of hard rock, just as if it had been deposited by water.

35.22 Sedimentary rocks are made of material from previously existing rocks broken down by mechanical and chemical weathering. Mechanical weathering includes alternate heating and cooling, expanding ice and root penetration. Chemical weathering includes acid and alkali salts in rainwater and groundwater, and organic compounds from decaying animals and plants. Particles from previously existing rocks form sediments that become compacted and cemented together. However, before these processes of rock formation, rock particles may be transported by wind or water. Sedimentary rocks may have a banded or layered appearance, are usually less compact than igneous rocks and may be crumbly. If you breathe on them, the added moisture may give the rocks an earthy smell. Sediments consisting of broken particles of the parent rock are called clastic, e.g. sandstone. Cementing agents include silica, calcium carbonate and iron oxides. The most common minerals in the fragmented rocks are quartz, feldspar, and clay minerals. Some sedimentary rocks were precipitated from solution, e.g. limestone, calcite and dolomite. Sea shells and corals form sedimentary rocks from the calcium carbonate.

35.22.1 Sandstone is made up of grains of quartz, SiO_2, with particle size up to 2 mm diameter and a texture like a sugar cube. It may also contain other particles of feldspar, garnet, tourmaline, and flakes of mica. It also contains substances acting as cement. Sandstone is still used for buildings because it may be plentiful in some places, e.g. Sydney, Australia, and is easy to saw and carve. Old sandstone buildings have a straw colour but that may be spoilt by atmospheric pollution.
Use a magnifying glass to examine the sandstone in any sandstone buildings or walls in your area.

35.22.2 Breccia has a rough, angular appearance because the stones contained within it are angular, with sharp edges. Breccia is usually formed at the base of cliffs in mountainous regions, where there is much rough, broken stone, scree. The scree is cemented into a hard mass with sand and clay. Breccia has little commercial value except as fill but the igneous breccia of South Africa contain diamonds.

35.22.3 Chalk, CaCO₃, is a soft white limestone, containing about 98% calcium carbonate, with the remainder usually made up of quartz. Most chalk consists of broken-down skeletons of sea shells. Flint nodules made of silica solutions within some chalk deposits are hard and brittle. Chalk is used in the manufacture of cement and lime. The white cliffs of Dover in England are made of chalk. Calcium carbonate occurs in calcite, marble, pearl, coral, egg shells, white wash, calcimine (kalsomine) and seashells. However, the blackboard chalk used in schools is calcium sulfate, CaSO_35.2H₂O.

35.22.4 Clay consists of decomposed weathered rock, usually granite, or others that contain feldspar. Pure clay is a dazzling white, has a soft, oily feel and is easily broken. Damp clay is sticky and has a special smell. It absorbs water and becomes plastic when wet. Clays do not split along bedding planes, i.e. a surface parallel to the original deposition surface. It has particle size less than 0.004 mm diameter, 1/256 mm. Clay minerals can take up or lose water according to temperature and amount of available water. Modelling clay, Plasticine, plastilina, is manufactured for use mainly by children.
Clay minerals include the following groups:
1. Illite, KAl₄(Si, Al)₈O₂₀(OH)₄, is the most common clay mineral.
2. Kaolinite, Al₂(OH)₄ (Si₂O₅), known as white clay, pipe clay, ball clay and China clay, is used for making pottery.
3. Montmorillonite, smectite (Na, Ca)(Al, Mg)₆(Si₄O₁₀)₃(OH)₆.nH₂O, forms from volcanic ash and occurs in Fuller's earth and bentonite. These minerals easily exchange cations and take up and lose water, so are called "swelling clays". Bentonite is often included in products to improve the water holding capacity of soil because of its water absorbing and water retaining properties.
4. Vermiculite (Mg, Fe, Al)₃(Al, Si)₄O₁₀(OH₂).4 H₂O, is used as a potting medium in horticulture. The name comes from the property of forming long worm-like structures when heated.
Collect clay samples in your region. Make clay pots and leave them in the sun to dry. Note which clay makes the best pot. Examine samples of potting mix for the presence of vermiculite.

35.22.5 Conglomerate, puddingstone, consists of pebbles rounded by water action, cemented together by hardened clay or sand. The pebbles are mainly quartz granite limestone and basalt. Conglomerate occurs in the flood plains of old river valleys beaches and the outwash fans where a river joins a lake or sea. The lower layers of these beds become compressed and cemented to form conglomerate. The conglomerate formed by the grinding action of glaciers is called tillite. The particles in tillite may be so fine that they are rock flour. Conglomerate is seldom used as a building material because of its uneven texture. However very large rounded stones and small white pebbles may be extracted from conglomerate and used for decoration.

35.22.6 Gypsum, CaSO_35.2H₂O, has white to grey colour depending on impurities, hardness 2, white streak, white to grey glassy to pearly lustre, good cleavage in one direction, relative density 2.32. It forms by evaporation as large, clear crystals, selenite, that break into plates with a glistening or pearly appearance. Rock gypsum contains some lime and sodium chloride. Gypsum occurs in the beds of lakes, mixed with sand and clay washed into the depression after the formation of the gypsum. To make plaster of Paris, gypsum is heated to form the hemihydrate, CaSO35.1/2H₂O, then mixed with water A form of gypsum called alabaster is carved and polished for ornaments. About 4% of the mixture used to make Portland cement is gypsum. Gypsum has low thermal conductivity so is used as a filler insulator in buildings. Scratch the specimen with a fingernail, but note that it is not as soft as talc. Crystals are flexible but not elastic, so they do not return to the previous shape.
Lustre: non-metallic, vitreous, also pearly or silky

35.22.7 Limestone, CaCO₃, is made up of the shells and skeletons of tiny organisms that once lived in the seas. These organisms extracted calcium carbonate from the sea water and built up beautiful microscopic structures. These sank to the seabed when the organisms died, and decayed there. Dead organisms formed deposits thousands of feet thick. With later earth movements, the limestone layers were uplifted and exposed above the water's surface. Limestone is now quarried and used in the manufacture of cement.

35.22.8 Mudstone and siltstone are intermediate stages between clay and shale, 1/16 to 1/256 mm diameter. They do not split into bedding planes. However, they do split into plates and are easily rubbed back to mud or silt if moistened with water. They are soft and silky to touch and dissolve easily so are not often used as a building stone. Mudstone may contain fossil impressions of plants and animals. Marl is a calcareous mudstone. In China, fine silt has been deposited by wind to form loess.

35.22.9 Shale splits easily into bedding planes parallel to the orientation of the clay mineral particles. Shales do absorb water and become plastic when wet, but may disintegrate under water. The colours are pink to yellow and brown to grey. Shales may contain fossils and have an earthy smell. Under great pressure, shale forms slate. Oil shales are brown to green fine-grained shales rich in carbon-based substances. Oil can be extracted from these light weight shales by heating. A cut with a knife leaves a greasy mark that is darker than a freshly broken piece of shale. Pieces of oil shales may burn with a smoky flame that smells of kerosene. Exposed oil shales turn white and split into layers.

35.23 Metamorphic rocks are the result of heat and pressure applied to igneous and sedimentary rocks. The pressure causes mineral grains to align in a single plane so the rock tends to split in this direction. This alignment is called foliation. However, marble and quartzite are metamorphic rocks but are not foliated. Metamorphic rocks are similar to igneous rocks in that they are hard and have interlocked mineral grains. Thermal metamorphism, contact metamorphism, is caused by heat when molten lava heats rocks to form fine grain rocks with no bands or layers, e.g. hornfels. Regional metamorphism refers to the changes caused by extensive heat and pressure to produce coarse grain, banded rocks, e.g. gneiss.
The three varieties of foliation are as follows:
1. Gneissic or banded foliation shows distinct bands of different minerals. The thicker bands are usually feldspar.
2. Schistosis foliation is caused by the parallel arrangement of platy minerals, e.g. mica.
3. Slaty cleavage refers to the tendency of a rock to split into thin, even slabs, e.g. slate.
The cleavage is the result of the parallel planar arrangement of microscopic mineral grains.

35.23.01 Classification of metamorphic rocks
1. Foliated, banded or platy:
1.1 Coarsely banded, bands irregular in thickness - gneiss
1.2 Schistose, regular banding, medium in thickness, and platy - schist
1.3 Slaty regular fine banding and platy - slate
2. Non-foliated, massive or granular:
2.1 Mainly calcite or dolomite - marble
2.2 Mainly quartz - quartzite
2.3 Mainly serpentine and / or talc - serpentine or talc
2.4 Mainly organic, grey or black - graphite and anthracite coal

35.23.1 Coal is mainly carbon from woody material, algae and any plant debris that collected millions of years ago in swamps. The heat and pressure caused by overlying deposits of sand and clay caused the formation of coal. The older the coal the greater the percentage of carbon. Peat is a lowest quality coal. It has a high percentage of water. Lignite or brown coal is older than peat and has received much more compression. Bituminous coals are hard, black and brittle. Anthracite is black and shiny.
Collect different types of coal and break them with a hammer. You may find fossils in the peat and softer coal. Anthracite breaks with a conchoidal (shell-like) fracture similar to when you smash the corner of a piece of glass. Find the weight and volume of the coal samples and calculate the density Burn the coal samples to heat waters and estimate that sample produces the most heat per gram of coal.

35.23.2 Graphite, like diamond, consists of the crystallized carbon, C. Graphite has metallic lustre, can mark paper, grey to black colour, black streak, cleavage in one direction, and relative density 2.1. It is soft, black and opaque. It is greasy to touch and leaves a grey dust on the fingers so it is a good lubricant for machinery and "lead" pencils. The softer lead pencils, the "B" grade, contain more graphite in the "lead". By contrast diamond is crystallized carbon but it is one of the hardest minerals and is colourless and transparent. Graphite is a good conductor of electricity but diamond does not conduct electricity. Graphite is also used as stove polish and dry lubricants in the electrical industry. It occurs in crystalline igneous and metamorphic rocks and is also made artificially by heating coke in a furnace. The central electrode of a dry cell battery is made of carbon.

35.23.3 Marble, CaCO₃, is a crystalline limestone formed by the heating of limestone rock under pressure, thermal metamorphism. If limestone is heated strongly, it gives off carbon dioxide leaving quick lime, calcium oxide, CaO. If limestone is heated under great pressure it melts and does not lose carbon dioxide. If it then cools slowly, it recrystallizes as marble. Marble is a beautiful building stone, valued for its smoothness and hardness. Pure white marble is recrystallized calcite and looks like a sugar cube. Different colours in marble are caused by impurities, e.g. dolomite, silica, iron, clay minerals. A common method of preparing carbon dioxide is to add hydrochloric acid to marble chips. Not all polished stones are marbles.

35.23.4 Petroleum, crude oil, is a mixture of hydrocarbons often with sulfur and nitrogen. Most scientists think it was formed from the remains of marine organisms buried at great depths, although some people suggest an inorganic origin. Oil deposits usually occur in sedimentary rocks with a thick layer of rock above and below. The oil may float on a layer of water and be under a layer of natural gas, a mixture of gaseous hydrocarbons, mainly methane. Crude oil is usually a dark green, brown or black oily liquid with a characteristic smell. It always occurs with gas and water. A waxy form of petroleum is made from coal.

35.23.5 Quartzite is an altered and exceedingly hard sandstone. The grains have been bound together by a cement formed by the dissolving action of heated water. The constituent grains have been recrystallized to form dense interlocked cementation. When sandstone is broken, only the cement holding the sand grains together is damaged. If a piece of quartzite is shattered, both the sand grains and cement are broken because the particles are so strongly bound together. Quartzite has a glistening appearance caused by its sugar-like crystal structure. Quartzite is white when pure, but most of it contains mica, iron, feldspar or other mineral particles that alter the colour to grey, brown, red, yellow, green or black. Owing to its extreme hardness, quartzite has few commercial uses except road-making.

35.23.6 Slate is a dense rock with a texture so fine that the individual grains in it cannot be seen by the eye or even through a magnifying glass. Slate comes from clay, mudstone and shales altered by heat and pressure. It was once laid down as alluvial material at the bottom of lakes and oceans. Fossils of long dead marine plants and animals can be seen perfectly preserved in it. Most slate is grey, dark grey or black, depending on how much plant material it contains. It may also be green because of the chloride in sea water, or red, purple, yellow or brown because of iron stains. Slate has a well-marked cleavage so the surface of the flat broken piece of slate feels soft and silky. Although easily cut, slate resists the weather so it is for roofs. Formerly, school children learnt their lessons on small slate boards that they could write on with chalk and later erase the writing.

35.23.7 Talc, Mg₃Si₄O₁₀(OH)₂, has green to yellow to white colour, hardness 1, white streak, pearly to greasy lustre with a silvery sheen, good but not visible cleavage, greasy to touch, relative density 2.7 to 2.8. Talc forms as a secondary mineral after metamorphosis. Pieces of talc break into distinctly thin, easily bent layers that remain in that shape. So talc is flexible but not elastic. Talc occurs as compact masses, not crystals. Talc is used to make talcum powder, dry lubricants, fireproof materials, linoleum, paper filler and floor coverings. Soapstone is a compact form of talc used for carving. Tailors use small pieces of talc, French chalk, to mark cloth.
Handle a talc specimen and note that it has a pearly surface, is greasy to touch, and can be easily scratched by the fingernail. Use it to mark paper.

35.24 Make artificial igneous rocks, alum crystals, sulfur crystals
1. Crystallization of alum solutions is similar to the formation of coarse grained and fine grained igneous rocks. Fill a test-tube one quarter full of powdered potash alum, [Al₂(SO₄)₃.K₂(SO₄).24H₂O] [also shown as KAl(SO₄)₂.12H₂O]. Slowly add just enough boiling water to dissolve the alum. Hold the test-tube in a flame so that the mixture boils gently. 1. Pour half the solution into a shallow metal container. Place a piece of string partly in the liquid and add a seed crystal. Stir the alum solution in the container so it cools quickly. 2. Hang another piece of string in the test-tube so that it reaches the bottom and add a seed crystal. Place the test-tube where it will cool slowly. Examine the two solutions the following day and note the sizes of the crystals formed.
2. Melt some sulfur in a test-tube. Fit a filter paper into a funnel and pour the molten sulfur into it. As the sulfur cools it begins to solidify, first forming a crust on the surface. As soon as the crust has formed, remove the filter paper from the funnel and unfold it, so that the still liquid sulfur in the lower part of the filter can flow away from the crust. Note a mass of small crystals on the underside of the crust. Use a magnifying glass to observe the shape of these crystals.
3. Melt sulfur in a test-tube then pour it into a large beaker of water so that it solidifies rapidly to form plastic sulfur. Take it out of the water and examine it after two hours. The solid sulfur formed is very hard and you cannot see crystals with a magnifying glass. However, very tiny crystals may be seen with a microscope.

35.25 Making artificial rocks, sedimentary rocks
1. Use a hammer to grind different coloured sedimentary rocks, keeping the colours separated. Put coloured powdered particles in a glass jar as different layers. Let water trickle down the inside of the jar so as not to disturb the layering until the water is 1 cm above the sediments. Put the jar in the sun and let the water evaporate. Wrap the jar in a thick cloth and break it with a hammer.
2. Mix Portland cement with water and put it in a mould until it hardens. Break the set cement with a hammer and examine the outside and inside surfaces.
3. Mix dry cement with twice as much sand or gravel to form concrete. Add water, mix thoroughly, and place it in a mould. Leave the concrete to harden for several days. Break the set concrete with a hammer and examine the outside and inside surfaces. Note whether the concrete is easier or harder to break than the Portland cement.
4. Mix plaster of Paris with a small amount of water and put it in a mould until it hardens. Stir rapidly or it will harden while being mixed. Break the set plaster with a hammer and examine the outside and inside surfaces. Note whether the plaster is easier or harder to break than the Portland cement or the concrete.

35.26 Making artificial rocks, metamorphic rocks
Fire a shaped piece of clay that has first been dried and put on a piece of broken pottery and heated it in a large crucible over a Bunsen burner.

35.27 Folds
See diagram 35.27: Folds
Folds occur where parallel layer form an arch, anticline, or form a trough, syncline. The line along which the direction of dip changes is the hinge line. Arrange carpets or blankets in layers on the floor. Push the layers horizontally to create anticlines and synclines.

35.28 Joints
Joins are fractures in rocks where no relative movement occurs each side of the fracture. Joints can be caused by cooling shrinkage and increased tension within the rock.

35.29 Faults
See diagram 35.29: Faults
A fault is a fracture in rock where some displacement has occurred. The fault plane of the fracture can be vertical but usually there is a dip of the fault. Dip-slip movement is where the direction of movement on the fault plane, is parallel to the dip of the fault, i.e. up or down. Strike-slip movement is where the direction of movement on the fault plane is parallel to the strike of the fault, i.e. sideways. This movement results in tear faults. The throw of a fault is the vertical displacement between blocks of rock. The heave of a fault is the horizontal displacement of blocks of rock. The hanging wall is the surface with rock above it. The footwall is the surface with rock below it. A normal fault is a dip-slip fault with the hanging wall on the downthrow side, i.e. it appears that a block has slipped down the fault. A reverse fault is a dip-slip fault with the hanging wall on the upthrow side, i.e. it appears that a block has been pushed up the fault. A trough fault is caused by downthrow movement between two parallel faults to form a graben or rift valley. Upthrow between two parallel faults results in a horst. A series of parallel faults is called step faulting.
Make layers of modelling clay, Plasticine. Cut the layers vertically then cut the layers at an angle to create a model of a fault.

35.30 Examine sand with a magnifying glass
The nearly colourless crystals are probably the mineral quartz. Look for other minerals in the sand.

35.30.1 Quicksand
Areas of quicksand have a source of upwards pressure from a spring below. The sand becomes suspended and frictionless so will not support weight on it. A person caught in quicksand should try to float on the back and keep the arms below the surface. The nose and mouth should remain above the surface and allow a slow and laborious paddling to the edge of the quicksand.

35.31 Tests for limestone
Drop lemon juice, or vinegar, or dilute hydrochloric acid on rock specimens. Limestone will effervesce or bubble caused by carbon dioxide gas given off. Marble, a metamorphic rock made from limestone, will also respond to this test.

35.32 Sort sediments
Thoroughly mix equal portions of gravel, coarse sand particles, and clay particles. Place this mixture in a glass jar, not more than half full. Fill the jar with water. Place a cap on the jar and shake vigorously. Allow the material to settle. The components will arrange themselves in order, with the heavier particles at the bottom and the clay particles on the top.

35.33 Piezoelectricity
See also 32.1.2: Pressure, piezoelectricity (Electronics)
The minerals tourmaline and quartz have piezoelectric, pyroelectric, properties. Temperature or pressure changes cause such minerals to get an electric charge when they are warmed or cooled or pressed. Demonstrate piezoelectricity by dusting the cooling or warming crystal with a dust of red lead and sulfur that has passed through a silk or nylon screen. A simple bellows can be made from a plastic nasal spray or deodorant bottle in that the aperture has been enlarged to allow a sizeable spray to be emitted. Place in the bottle a mixture of about 2 parts red lead to 1 part sulfur. Put a small piece of silk or nylon stocking over the mouth of the bottle. Tighten this with a rubber band. The dust particles receive electric charges as they pass through the screen formed by the stocking. They settle on the end of the crystal that attracts them. The red lead gets a positive charge and goes to the negative end of the crystal. The sulfur gets a negative charge and settles on the positive end of the crystal.

35.34 How fossils form
A fossil is any evidence of a form of life that lived some time in the past. Most fossils are found in layers of sedimentary rock. Fossils formed by burial are usually found when the sedimentary rock containing them is split open. Cover a leaf with petroleum jelly and place it on a pane of glass or other smooth surface. Make a circular mould about 2 cm deep and place it around the leaf. Hold the mould in place by pressing modelling clay around the outside. Now mix up some plaster of Paris and pour it over the leaf. When the plaster has hardened, you can remove the leaf, and you will have an excellent leaf print. Some fossils were made this way by having silt deposited over them, which later hardened into sedimentary rock. Repeat this experiment using a greased clam or oyster shell to make the imprint.

35.35 Find fossils
In some localities, fossils may be found in stone quarries or where there are rock outcrops. Try to find someone in the community who knows about fossils and then plan a field trip with the class to collect some of them. If there are no fossils in your locality, you may have to depend on state or national museums to send you a few. A letter to the state or national museum may prove helpful.

35.12.1 Touchstone
A form of schist used to assay gold by comparing the streak of the sample to the streak of "touch needles" with known gold content.

35.14.3 Amethyst
A violet-blue variety of quartz. (Greek: not intoxicate, amethyst was thought to be a charm against inebriety)

35.14.4 Chalcedony
It is fibrous with very small crystals of quartz and the silca mineral moganite. Chalcedony may be in the form of the following gemstones: Agate, Aventurine, Bloodstone, Carnelian, Chrysoprase, Heliotrope, Jasper, Onyx, Sard
Agate is concentrically banded in crazy patterns it is called agate. Onyx is in flat layers. Sardonyx is in the form of white and brown red bands. Cornelian is red due to iron impurities. Thunder eggs are in the form of a rock shell filled with agate.