UNPh35

School Science Lessons
Earth sciences experiments, geology
2009-11-10
Please send comments to: J.Elfick@uq.edu.au

Geology
Minerals
Key to MINERALS,(internet) Suzanne D. Golding, University of Queensland
Index items A to B
Index items C
Index items D to H
Index items I to N
Index items O to P
Index items Q to S
Index items T to Z

Some content is based on A Field Guide in Colour to Minerals, Rocks and Precious Stones, Dr Jaroslav Bauer, Octopus Books Limited.

Table of Contents
35.1.0 Collecting and identifying
35.5.0 Physical properties of minerals
35.13.0 Other tests
35.14.0 The main rock-forming minerals
35.20.0 Other minerals and ores
9.9.18 Hydroponics, soil-less culture solutions, Knop's solution, mineral deficiency experiment
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 and technical information
Soils

35.1.0 Collecting and identifying
35.1 Fieldwork
35.1.1 Measure dip and strike, direction of a stream
35.1.2 Visit an outcrop or quarry, lode
35.2.0 How to examine a mineral or a rock
35.3.0 Abundance of elements in the Earth's crust
35.4 Rocks and minerals, classification, origin

35.5.0 Physical properties of minerals
35.5 Colour
35.6 Lustre (metallic lustre, non-metallic lustre)
35.7 Transparency (transparent, translucent,opaque, refraction)
35.8 Crystal systems, crystal habit
35.9 Cleavage, fracture twin crystals, crystal faces
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 and taste
35.13.4 Luminescence
35.13.5 Grain size and roundness
35.13.6 Feel and conductivity

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
27.6.4.1 Calcite crystals (physics)
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
35.17 Actinolite
35.20.1 Anglesite (lead sulfate)
35.20.2 Antimony, Sb
35.20.3 Argentite, Ag₂S
35.20.3 Asbestos (hydrous magnesium silicate)
35.20.3.1 Meerschaum
35.20.4 Azurite (basic copper carbonate)
35.20.4a Bauxite
35.20.5 Bornite, bournonite [Also Cu₂S (chalcocite) and CuS (covelite)]
35.3.3.1 Bustamite (calcium manganese silicate)
35.20.6 Cadmoselite, rare cadmium mineral containing cadmium (II) selenide, CdSe
35.20.7 Cassiterite, SnO₂,
35.20.8 Cerussite (lead carbonate)
35.20.9 Chalcopyrite, copper pyrite (copper iron sulfide)
35.20.9a Chromite, Fe₂Cr₂O₄, chrome iron ore, chromium ore, in peridodites, serpentines
35.20.10 Cinnabar, HgS, mercury (II) sulfide
35.20.11 Copper, Cu
35.20.11.1 Copper glance, copper (I) sulfide, Cu₂S, chalcocite
35.20.12 Coronadite (lead manganese oxide)
35.20.12.1 Corundum, Al₂O₃
35.20.13 Cryolite (sodium aluminium fluoride)
35.20.13a Emery
35.20.14 Fluorspar, fluorite (calcium fluoride)
35.20.15 Galena (PbS, lead (II) sulfide)
35.3.3.3 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, FeTiO₃35.17 Jadeite
35.20.21a Kalinite
35.20.21b Kyanite
35.20.22 Lead, Pb
7.2.2.23a Lead paint
7.2.2.23b Tetraethyl lead
35.20.23 Magnetite, Fe₃O₄
35.20.24 Malachite (copper carbonate)
Mascagnite, ammonium sulfate
35.20.25 Marcasite, FeS₂
35.20.26 Mercury, Hg
35.20.27 Millerite, NiS
35.20.28 Molybdenite, MoS₂35.17 Nephrite
35.20.29 Nickel, Ni
35.20.30 Nickeline, niccolite, NiAs
35.20.31 Platinum, Pt
35.20.32 Pyrite (iron sulfide)
12.8.8 Pyrite, heat iron (II) sulfide,(FeS₂pyrite, fool's gold)
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 and calamine (basic 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
35.20.51 Zincite

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
35.2.4.1 Scoria
35.21.5 Rhyolite
35.21.6 Serpentine
35.21.7 Tuff

35.22.0 Sedimentary rocks
35.22.1 Sandstone
35.22.2 Breccia
35.22.3 Chalk
6.43 Chalk (lime) content of the soil
35.22.4 Clay
35.22.5 Conglomerate (puddingstone)
35.22.6 Gypsum, (calcium sulfate) plaster of Paris
35.22.6.1 Alabaster
3.67 Strength of plaster of Paris
35.22.7 Limestone, stone dust
35.22.7.1 Calcium carbonate dissolves in rain water
35.22.8 Mudstone, siltstone, marl, loess
35.22.9 Shale
35.39 Make clay pots (Primary)
4.33 Make sedimentary rocks (Primary)

35.22.4 Clay
35.22.4.01 Chemical weathering
35.22.4.1 Illite
35.22.4.2 Kaolinite
35.22.4.3 Montmorillonite (smectite)
35.22.4.4 Bentonite
35.22.4.5 Fuller's earth,
35.22.4.6 Vermiculite
35.22.4.7 Halloysite

35.23 Metamorphic rocks
35.23.01 Classification of metamorphic rocks
35.23.1 Coal
35.23.2 Graphite
35.23.3 Marble, CaCO₃
35.23.4 Petroleum, crude oil
35.23.5 Quartzite
35.23.6 Slate
35.23.7 Talc Mg₃Si₄O₁₀(OH)_2, MgSi₈O₂₀(OH)₄
4.32 Weathering rocks (Primary)

35.24 Make artificial igneous rocks,alum crystals, sulfur crystals
35.25 Making artificial rocks,sedimentary rocks
35.26 Making artificial rocks,metamorphic rocks
6.36 Candle "lava" (Primary)
12.16.6.01 Prepare an imitation volcano with baking soda

35.27.0 Collecting rocks
35.27 Folds
35.28 Joints
35.29 Faults
35.30 Examine sand with a magnifying glass
35.30.1 Quicksand
35.31 Tests for limestone
35.32 Sort sediments
35.33 Piezoelectricity
35.33.1 Pyroelectricity,ferroelectricity
35.33.2 Dimorphism, aragonite
35.34 How fossils form
35.34.1 Dendrites, false fossils
35.35 Find fossils
1.32 Different rocks (Primary)
2.36 Rocks with a magnifier (Primary)
5.33 Collect rocks (Primary)
35.21.8 Classify igneous rocks in hand specimens

35.40.1 Mapping contours, geological structures, erosion
35.40.2 Isostasy models

35.28.0 Equipment and technical information
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)

Appendix 1: Chemicals by chemical name
Appendix 2: Low-cost chemicals and common substances
Appendix 3: Preparation instructions for acids and bases
Appendix 4: Preparation instructions for reagents
Appendix 5A: Flammable liquids
Appendix 5B: Poisons
Appendix 6: Abbreviations
Appendix 7: Prefixes and suffixes
Appendix 8: Hazard classifications
Acid-base indicators
Laboratory safety
Safety equipment
Periodic table
Table of the elements

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, direction of a stream
See diagram 35.1.1: Dip and strike, direction of a stream
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.
The direction of a stream that became dry many years ago can be seen if one rock was in a position to prevent the movement of another rock.

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, classification, origin
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.
Minerals can be classified as:
1. Elements
2. Sulfides (selenides, tellurides, arsenides, antimonides, bimuthides)
3. Halides
4. Oxides, hydroxides
5. Nitrates, carbonates, borates
6. Sulfates (chromates, molybdates, wolframates)
7. Phosphates, arsenates, vanadates
8. Silicates
9. Organic substances
Origin of minerals
1. Crystallization from magma, e.g. magnetite, mica, quartz,
2. Physical, chemical and biological changes caused by weathering, e.g. serpentine, malachite
3. Sedimentaryand evaporation processes, e.g. rock salt, calcite
4. Biological accumulation of salts, e.g. limestone, pyrite

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". The names of some colours come from the characteristic colour of minerals, e.g. emerald, ruby, azure, amethyst. Quartz, calcite and rock salt are colourless if they do not contain impurities. However some pure minerals may have different colours, e.g. fluorspar, apatite and beryl. The colour of some minerals may be changed by sunlight, artificial light, ultraviolet light, turning in the light, radioactivity, surface tarnish, heat, and dyes.

35.6 Lustre
The lustre is the appearance of the surface of a mineral in reflected light, depending on the reflection and refraction of light.
Minerals may be:
1. opaque and with a metallic lustre, like a metal, e.g. pyrite, galena,
2. opaque or transparent but without a metallic lustre, subdivided as:
2a. adamantine (diamond-like) lustre, vitreous (glassy) lustre, greasy (oily) lustre, dull lustre, silky lustre, e.g. asbestos and pearly lustre (layered).
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. You can read through a transparent mineral, e.g. quartz (rock crystal), rock salt, topaz. Translucent minerals allow passage of some light, but not images, like frosted glass used in bathrooms. Translucent minerals may be a transparent mineral containing impurities or finely granular transparent minerals. The minerals gypsum and mica may be translucent or opaque if finely granular but transparent if big crystals. Opaque minerals allow no passage of light and have a metallic or dull lustre.
Each mineral has a characteristic refractive index. An anisotrtopic crystal may split incident light to produce double refraction, e.g. calcite crystal

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 | See diagram 35.8 4: Crystal form of the seven crystal systems
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.
Crystallographic axes
When looking at a crystal, "axis a" is 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 and examples of crystal form (geometric shape of the crystal):
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
5. 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 relative width and length of the crystal faces (development of the faces of a crystal) and includes:
pyramidal, e.g. native sulfur, columnar, tabular (flat slab), e.g. mica, acicular (needle-like), fibrous, lamellar (plate-like), prismatic (elongated), e.g. most silicates.

35.9 Cleavage, fracture, twin crystals, crystal faces
See diagram 35.9: Twin crystals, striations, cleavage
Cleavage
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. The direction of cleavage may be indicated by fine cleavage rifts running along the planes of cleavage. Some fine grain rocks have a cleavage, e.g. slate.
Fracture
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).
Twin crystals
Crystals may be twinned in a regular way with internal angles consistently at more than 180^o, e.g. fluorite, gypsum, cassiterite.
Crystal faces
These faces may have characteristic striations, e.g. pyrite, quartz and tourmaline.

35.10 Hardness, Mohs' scale of 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. This hardness test can be applied only to fresh unweathered specimens. The columnar mineral kyanite is unusual because has hardness 4-4.5 vertically but hardness 6-7 horizontally. Fibrous and porous aggregates may have a deceptively lower harness because of the spaces between grains. Determining the hardness of earthy minerals, fine-grain minerals and needle-shaped fibrous minerals is almost impossible. 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 4.0. 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 tile or unglazed porcelain to leave a coloured scratch. Porcelain has Mohs hardness 6-6.5 so harder minerals will only leave a streak of white porcelain powder. Grind the harder minerals to see the streak colour. The colour of the streak may be different from the colour of the gross mineral in the ground. Colourless and white minerals always have white streak. Minerals with metallic lustre show the greatest difference between the true colour of the mineral and streak colour, e.g. black haematite gives a red streak powder. A mineral usually has a constant streak colour even if the colour of the mineral varies. So streak is much more reliable quality than colour of the mineral.

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 Ca(CO₃).Mg(CO₃), witherite BaCO₃, malachite CuCO₃Cu(OH)₂.

35.13.2 Magnetism test
See 4.67.0: Magnetism
Note whether the powdered mineral is strongly or weakly attracted to a magnet, e.g. magnetite Fe₃O_{4
attracts iron dust. Haematite becomes magnetic when heated.}

35.13.3 Odour and taste
See 16.3.4.1b: Earth smells, rain smells and cut grass smells, geosmin
Some minerals have a characteristic odour when rubbed, e.g. arsenopyrite, fluorite. sulfur has a distinctive odour and clay minerals have an "earthy" smell.
Minerals soluble in water have a characteristic taste. Some common examples include the following:
Borax, sweet alkaline taste, hydrated sodium borate, di-sodium tetraborate (III)-10-water (borax), Na₂B₄O₇.10H₂O
Chalcanthite, sweet metallic taste and slightly poisonous, CuSO₄.5H₂O, it is a water-soluble sulfate
Epsomite, epsom salts, bitter taste, MgSO₄.7H₂O, hydrated magnesium sulfate
Glauberite, bitter and salty taste, Na₂Ca(SO₄)₂, sodium calcium sulfate
Halite, rock salt, saline taste, NaCl
Hanksite, salty taste, Na₂₂K(SO₄)₉(CO₃)₂, sodium potassium sulfate carbonate
Melanterite, sweet, astringent and metallic taste, FeSO₄.7H₂O, hydrated iron sulfate,
Sylvite, (sylvine) bitter taste, KCl
Ulexite, alkaline taste, NaCaB₅O₆(OH)₆.5H₂O, hydrated sodium calcium borate hydroxide
Some people claim that the amalgam fillings in their teeth allow them to taste certain minerals. A "metallic taste" in the mouth may be caused byantibiotics, drugs, oral diseases and even mercury poisoning. Usually the metallic taste disappears within days.

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, phosphorus (V) oxide (phosphorus pentoxide), fluorite, calcite.

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.

35.13.6 Feel and conductivity
Experienced handlers of minerals, e.g. gemstone workers, claim to be able to recognize minerals from the feel against the fingers or the cheek. For example they say that talc and graphite feel smooth and greasy while kaolin (China clay) and chalk feel rough and dry. Copper feels colder than amber against the cheek because copper is a better conductor of heat. Similarly, they can distinguish real gemstones from glass imitations by feel against the cheek.

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. Quartz may exhibit characteristic striations on the surfaces of the crystal faces. 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)₂SiO₄2.Beryl, Be₃Al₂(SiO₃)₆
3. Pyroxenes, MgSiO₃, e.g. augite, jadeite, diopside
4. Amphiboles, e.g. hornblende NaCa₂(Mg, Fe²⁺, Fe³⁺,Al)₅(Si,Al)₈O₂₂(OH,F)₂, actinolite Ca₂(Mg,Fe²⁺)₅(Si₈O₂₂)(OH,F)₂
5. Micas KAl₂(Si₃Al)O₁₀(OH, F)₂
6. Talc, Mg₃Si₄O₁₀(OH)₂
7. Feldspars, KAlSi₃O₈
8. Quartz, SiO₂

35.15 Feldspars group, "field stone", as alumino silicates of alkali metals and alkaline earths, has pink colour but red-green or yellow colour if impure and some are white, e.g. sodium feldspar or albite, 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, KALSi₃O₈
2. Sodium feldspar or albite, NaAlSi₂O₈
3. Calcium feldspar or anorthite, CaAl₂Si₂O₈4. Barium feldspar or celsian, BaAl₂Si₂O₈
Feldspars are divided into two groups:
1. 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, Jean-Baptiste Biot 1774-1863) 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, NaCa₂(Mg, Fe²⁺, Fe³⁺,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,Fe²⁺)₅(Si₈O₂₂)(OH,F)_2, that includes nephrite or nephrite jade, the jade popular in China. Nephrite jade, Ca₂(Mg,Fe)₅(Si₈,O₂₂)(OH,F)₂ is a fine grained massive variety of actinolite that is used for ornaments and sculptures. 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 forms from evaporation of sea water and 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. 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. Weathering of pyrite liberates sulfuric acid that may change calcite into gypsum and other sulfates.
In limestone caves, calcite occurs as stalactites hanging from the roofs of limestone caves and stalagmites that grow up from the floor.
Ca(HCO₃)₂ (aq) --> CaCO₃ (s) + H₂O (l) + CO₂ (g)
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)_,[MgCa(CO₃)₂]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. Used as a sources of magnesium and in lining furnaces.

35.19.2 Carbonates include the following:
1. Calcite, CaCO₃2. Dolomite, CaMg(CO₃)₂
3. Magnesite, MgCO₃
4. Siderite FeCO₃
5. 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 word is derived from the Greek meaning incombustible. 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 and formerly was widely used as a heat insulator, for packing and for fireproof garments and fabrics. 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. Actinolite, amosite, anthrophyllite and crocidolite are amphiboles. 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 and holders. A soft light coloured hydrated magnesium silicate found in Asian Minor, H₄Mg₂Si₃O_10. If 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.

35.20.4a Bauxite
Residual sedimentary mineral that contains alumina and other oxides of aluminium in the amorphous or crystalline state. So it is more a rock-like mixture than a mineral. Usually formed by weathering in tropical regions. It is the most important ore for production of aluminium. Bauxite has non-metallic lustre, white streak, no good cleavage, can be scratched by the finger nail, white to grey-brown colour, uneven fracture, relative density 2.0 to 2.6.
See: Aluminium Oxide

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 in that shape.
Note the twinning habit colour and density of the specimen.
Bornite may be a mixture of copper sulfides including Cu2S (chalcocite) and CuS (covelite).

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. It forms twin crystals
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. It weathers to form the secondary minerals limonite, malachite and azurite.
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 non-metallic 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.

35.20.12.1 Corundum, Al₂O₃, ruby contains Cr, saphire contains Fe and Ti, hardness 9
See: Aluminium Oxide

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.

35.20.13a Emery is the naturally occurring mixture of the mineral corundum, magnetite and others. It is very hard and is used as an abrasive both as powder or as blocks or wheels.

35.20.14 Fluorspar, fluorite, calcium fluoride, CaF₂, blue john, Derbyshire spar, 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. It can form twin crystals.
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 forms from evaporation of sea water. 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.

35.20.21a Kalinite
Commonly potassium alum, which is a combination of potassium and aluminum sulfates, Al₂(SO₄)₃.K₂(SO₄).24H₂O, KAl(SO₄)₂.11H₂O. It is very astringent and is used for purifying water. Soda alum or chrome alum are similar combinations where the potassium has been replaced by the corresponding metals.

35.20.21b Kyanite
Also disthene, munkrudite, cyanite, rhaeticite (white-grey kyanite). From Greek kyanos: blue, aluminosilicate mineral, Al₂[O]SiO₄, fhatdness 4 -7, colourless streak, vitreous lustre. Found in aluminium-rich metamorphic pegmatitesand sedimentary rock. Used in refractory and ceramic products, electrical insulators, abrasives, gemstones. Elongated, columnar crystals. Anisotropic, i.e. two different hardnesses on perpendicular axes.]

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, (iron (II) diiron (III) oxide, ferrosoferric oxide. triiron tetroxide, black magnetic iron oxide) 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 (II) carbonate, Cu₂(OH)₂CO₃ or CuCO₃.Cu(OH)₂, 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. Pyrite may exhibits characteristic striations on the surfaces of the crystal faces.
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 yellow-orange, 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 and calamine (basic zinc carbonate)
Smithsonite, basic 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. Calomine, is used in pink calomine lotion for treating sunburn.

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.

35.20.51 Zincite
Red oxide of zinc, ZnO, found in metamorphic weathered deposits.

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.Tourmaline may exhibits characteristic striations on the surfaces of the crystal faces.

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.

35.2.4.1 Scoria (Greek: rust) (cinder) is similar to pumice but it is macrovesicular (larger vesicles and thicker vesicle walls). It is usually dark brown to red in colour and is formed from basalt or andesite. It may be in the form of vulcanic bombs large enough to be used for decoration in gardens. Other wise is is used as a base in gas-fired barbecuses to retain heat and absorb dripped grease, aggregate to make lighter concrete blocks, aggregate sands for horticultural purposes and backfill around subterranean water pipes.

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 weathering. 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 (chert), made of silica solutions within some chalk deposits are hard and brittle. Chalk is used in industry in paints, putties, polishes, rubber, crayons andin the manufacture of cement and lime. It is graded commercially according to colour, fineness and purity. The white cliffs of Dover in England are made of chalk. Calcium carbonate occurs in calcite, aragonite, marble, pearl, coral, egg shells, white wash, calcimine (kalsomine) and seashells. However, the blackboard chalk used in schools is calcium sulfate, CaSO_4.2H₂O.

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_4.2H₂O, 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 from evaporation of sea water as large, transparently 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. Gypsite is an earthy surface deposit. Satin spar is a silky fibre. To make plaster of Paris, gypsum is heated to form the hemihydrate (2CaSO4.2H₂O) then mixed with water. It can form twin crystals.
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.
Anhydrous calcium sulfate occurs as the mineral anhydrite.

35.22.6.1 Alabaster is a hydrous sulfate of gypsum, occurring in a very fine grained and translucent form. In the purest form it is snow-white but it occurs also coloured due to the presence of metallic oxides. It is found Europe and its softness allows it to be carved into sculptures and polished for ornaments.

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. Finely crushed limestone, called stone dust, is used in coal mines to render fine coal dust incombustible and prevent underground explosions.

35.22.7.1 Calcium carbonate dissolves in rain water
Rain water is weakly acidic and can dissolve calcium carbonate.
CO₂ (g) + 2H₂O (l) <--> H₃O⁺ (aq) + HCO₃^- (aq)
H₃O⁺ (aq) + CaCO₃ (s) <--> Ca²⁺ (aq) + HCO₃^- (aq) + H₂O (l)
CO₂ (g) + H₂O (l) + CaCO₃ (s) <--> Ca²⁺ (aq) + HCO₃^- (aq)

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.