School Science Lessons
35.1 Earth sciences, geology, clay, fieldwork, major groups of rocks, ores, silicates
2012-01-28
Please send comments to: J.Elfick@uq.edu.au
See: Chemistry index and minerals, alphabetical list of terms
Table of contents
35.1.0.0 Earth sciences, geology, clay, fieldwork, major groups of rocks, ores, silicates
35.22.4.0 Clay
35.1.0 Geology fieldwork
35.4.0 Major groups of rocks
35.3.1.0 Minerals mined at the Broken Hill mines, Australia
35.3.0 Ores and ore bodies
35.14.1 Silicates group, polysilicates, polysilicon
35.22.4.0
 35.22.4.0 Clay
35.22.4.8 Armenian clay
35.22.4.4 Bentonite
35.22.4.01 Chemical weathering reactions
7.6.1 Clay soils in water
7.6.3 Clay suspensions in a centrifuge
35.22.4.5 Fuller's earth
35.22.4.7 Halloysite, Al4Si4(OH)8O10.4H2O, clay mineral
35.22.4.1 Illite, KAl4(Si, Al)8O20(OH)4, KAl4(Si,Al)8O18.2H2O, most common clay mineral
35.20.21.1 Kaolinite, kaolin-type clays, Al4[(OH)8Si4O10]
7.6.2.1 Limewater with clay suspension
5.39 Make clay pots (Primary):
35.22.4.3 Montmorillonite (smectite)
7.6.2.2 Potassium alum or aluminium sulfate with clay suspensions
7.6.2 Salts with clay suspension
6.9.17.2 Soil acidity, (See 6. Clays, Clay soils)
9.7.1 Soil texture (See 2.1.2 Clay soil)
3.65 Strengths of mud, clay and sand bricks
35.22.4.6 Vermiculite, Mg2FeAl[(OH)2AlSi2O10Mg((H2O)4]
35.1.0 Geology fieldwork
35.1.1 Dip and strike, direction of a stream
35.30 Examine sand with a magnifying glass
35.29 Faults
35.27 Folds
35.34.1 Dendrites, false fossils
35.33.2 Dimorphism, aragonite
35.1.3 Examine a mineral or a rock
35.35 Find fossils
35.34 How fossils form
35.40.2 Isostasy models
35.28 Joints
35.40.1 Mapping contours, geological structures, erosion
32.1.2 Piezoelectricity
35.33.1 Pyroelectricity, ferroelectricity
35.30.1 Quicksand
35.32 Sort sediments
35.31 Tests for limestone
35.1.2 Visit an outcrop or quarry, lode
35.4.0 Major groups of rocks
35.21.0 Igneous rocks
35.23.0 Metamorphic rocks
35.22.0 Sedimentary rocks
35.21.0 Igneous rocks
35.21.8 Classify igneous rocks in hand specimens
35.21.01 Igneous intrusions, batholith, dyke, sill
35.21.3.1 Apatite
35.21.1 Basalt
35.21.2 Granite
35.24 Make igneous rocks
35.21.3 Pegmatite, beryl, topaz, tourmaline, zircon
35.21.4 Pumice
35.21.5 Rhyolite
35.21.5.1 Obsidian
35.21.5.2 Porphyry
35.2.4.1 Scoria
35.21.6 Serpentine
35.21.7 Tuff
35.23.0 Metamorphic rocks
35.23.2.1 Amber, C12H20O, succinite
35.23.01 Classify metamorphic rocks
35.23.1 Coal, coal dust explosions
35.23.1.1 Coal seam gas, CSG, and coal to liquid, CTL, projects
35.23.2 Graphite, diamond, C
35.26 Make metamorphic rocks
35.23.3 Marble, CaCO3
35.23.4.1 Oil shale and fracking (hydraulic fracturing)
35.23.4 Petroleum, crude oil
35.23.5 Quartzite, SiO2
35.23.6 Slate, (C + clay, mudstone, shales)
35.23.7 Talc, soapstone, talcstone, steatite, French chalk, Mg3Si4O10(OH)2, MgSi8O20(OH)4
35.22.0 Sedimentary rocks
35.22.6.1 Alabaster
35.22.10 Arenaceous rock, arenite
35.22.11 Argillaceous rock
35.22.2 Breccia
35.22.3 Chalk
35.22.5 Conglomerate (puddingstone)
35.22.6 Gypsum, (calcium sulfate) plaster of Paris
35.22.7 Limestone, stone dust
35.22.7.1 Calcium carbonate dissolves in rain water
35.25 Make sedimentary rocks
35.22.8 Mudstone, siltstone, marl, loess
35.22.1 Sandstone
35.22.9 Shale
35.3.0 Ores and ore bodies.
35.3.01 Primary ore deposits
35.3.02 Secondary ore deposits
35.3.03 Placer deposits
35.3.1.0 Minerals mined at the Broken Hill mines, Australia
35.20.22 Lead, Pb
35.20.50 Zinc, Zn
1.0 Ore minerals of the primary (sulfide) zone
35.20.15 Galena, lead (II) sulfide, lead sulfide, lead glance, blue lead, PbS
35.20.41 Sphalerite, zinc sulfide, zinc blende, mock ore, mock lead, black jack, ZnS
2.0 Gangue (waste) minerals of the primary (sulfide) zone
35.3.3.1 Bustamite, calcium manganese silicate, MnCaSiO6
35.3.3.3 Garnet, manganese aluminium silicate, (Mn3Al2Si3O12), Mn3Al2[SiO4)3, garnet, spessartine, spessartite
35.20.35 Rhodochrosite, manganese carbonate, manganese spar, MnCO3
3.0 Other minerals of the primary (sulfide) zone
35.20.9 Chalcopyrite, copper pyrites, copper iron sulfide, "copper sulfides", CuFeS2
35.20.32 Pyrite, FeS2, iron sulfide, iron disulfide, sulfuric pyrites, iron pyrites, fool's gold
35.20.34 Pyrrhotite. iron sulfide, magnetic pyrites, FeS
4.0 Ore minerals of the oxidized zone
35.20.1 Anglesite, lead sulfate, lead vitriol, PbSO4
35.20.4 Azurite, basic copper carbonate, blue carbonate of copper, 2CuCO3.Cu(OH)2
35.20.8 Cerussite, lead carbonate, ceruse, white lead ore, PbCO3
35.20.11 Copper, Cu, natural copper
35.20.12 Coronadite, lead manganese oxide, Pb2Mn8O16
35.20.17 Goethite, FeO(OH), hydrated iron oxide, hydrous iron oxide
35.22.6 Gypsum, (calcium sulfate) plaster of Paris
35.20.24 Malachite, copper carbonate, Cu[(OH)2.CuCO
35.20.33 Pyromorphite group, lead phosphate, Pb5(PO4)3Cl
35.20.39 Silver, natural silver, Ag
35.20.40 Smithsonite, calamine, zinc spar, galmei, ZnCO3, (basic zinc carbonate, ZnCO3.2ZnO.3H2O)
35.14.1 Silicates group, polysilicates, polysilicon
35.14.2 Opals, SiO2.nH2O
35.14.2.1 Opal valuation
35.14.3 Amethyst
35.14.4 Chalcedony
35.1.0 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 to measure elevation and gradients, or protractor and weighted thread, for measurement of 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 Dip and strike, direction of a stream
See diagram 35.1.1: Dip and strike, direction of a stream | See diagram 5.5.1: Dip and strike (Not labelled)
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 180o 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.
35.1.3 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.
35.3.0 Ores and ore bodies
See diagram 35.3.0: Alteration of an ore body
An ore is mineral containing a useful substance, usually a metal, that can be profitably extracted. An ore body is a connected mass of ore suitable for mining and is referred to by terms such deposit, seam, lode, reef, and placer.
35.3.01 Primary ore deposits
Native metals are metals found not combined with other elements, e.g. copper, gold, mercury, platinum and silver. Minerals may be from igneous rocks and found in faults or joints in the rocks or bedded like sedimentary rocks. The mineral may have been concentrated in the fluids that move from the main magma into the surrounding rocks then deposited in fissures when cooling. Minerals with high melting points and low solubility in water, e.g. cassiterite and molybdenite occur close to the margins of plutonic igneous rock, e.g. granite. However other minerals occur farther away from the igneous source, e.g. galena, stibnite and cinnabar. Gold may occur in veins close to an igneous rock or far away. Quartz, as a non-valuable gangue mineral, may occur associated with the above minerals or by itself. Iron may occur in bog deposits after being precipitated chemically by iron bacteria and the large occurrences of haematite, limonite and magnetite have been formed by metamorphism of these deposits. Metals deposited as sulfides on the sea floor include the bedded lead, zinc and copper sulfides of Mount Isa, Queensland and the lead, zinc and silver ore bodies of Broken Hill, New South Wales. Most minerals occurring as primary ore bodies are the sulfides and oxides of the metals and have a metallic lustre.
35.3.02 Secondary ore deposits
Weathering of a primary ore body may lead to the production of new minerals or change the concentration of metals in it. Oxidizing may occur above the water table because of the movement of oxygenated water through the soil but below the water table reducing may occur. So the upper zone of a secondary ore deposit may contain oxides, carbonates, sulfates or hydroxides of metals above secondary sulfides formed by reduction of earlier formed sulfates. However below the water table the primary sulfides and oxides are unaltered under the reducing conditions. Deposits rich in iron may have a gossan, iron cap, at the surface. However even inconspicuous outcrops of an ore body may contain minerals different from the original deposits. Deposits at Broken Hill, include silver-bearing galena with sphalerite and a large variety of gangue minerals formed by secondary alteration of the sulfides. Minerals that are soluble in water are found only where water is scarce, e.g. nitrates occur only in waterless deserts.
35.3.03 Placer deposits
The breakdown of the rocks and minerals by weathering and erosion may cause concentration of the more durable and dense minerals in the beds of streams, on beaches or in lakes, placer deposits. The most common minerals in placer deposits are gold, cassiterite, rutile, zircon, monazite, platinum and ozmiridium, and the gemstones diamonds and sapphires.
35.3.1.0 Minerals mined at the Broken Hill mines, Australia
The minerals of Broken Hill are world famous because many of them are rare and beautiful. Unfortunately, most of the rare minerals were found in the top sections of the mine where the sulfide ore minerals had been weathered and oxidized by groundwater to produce a dazzling array of secondary minerals. These areas of the mine are long worked out and not producing ore or mineral specimens anymore.
35.3.3.1 Bustamite
Bustamite, calcium manganese silicate, MnCaSiO6, also occurs in the galena-rich lodes. It has a range of pink to orange to deep brown colours..
35.3.3.3 Garnet (spessartine) manganese aluminium silicate (Mn3Al2Si3O12), is a port wine red mineral commonly associated with galena ore. Chalcopyrite, copper iron sulfide, occurs in veins in garnet, quartzite and garnet sandstone in ore bodies.
35.3.3.12 Coronadite
Coronadite, (lead manganese oxide), originally referred to as psilomelane, is massive, stalactitic, shawls, cellular, botryoidal habit. It is abundant in the upper levels of the oxidized zone and outcrop. The associated minerals are goethite that forms the matrix for a variety of secondary minerals.
35.14.0 Quartz, silica, (rock crystal, rose quartz, smoky quartz, milky quartz), SiO2
Quartz is a lattice of SiO2 tetrahedra, 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 and is probably the most abundant mineral on the earth. 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 (cornelian), chalcedony, jasper, onyx (Greek: finger nail), opal, rock crystal, milky quartz, rose quartz and smoky 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 is a commonly used cheap abrasive so is used in soap as sand soap to remove grease from the hands and in sandblasting to clean away dirt and smooth rough surface. Purple to violet quartz is amethyst. Yellow quartz is citrine. Fortune-tellers and people who think crystals have supernatural properties use quartz crystals.
1. Note the glassy lustre and hardness of the specimen.
2. Crystals may have piezoelectric properties so it develops electric potential under stress. When two crystals are struck together separation of charge in the crystal lattice can produce a very high voltage so quartz is used in barbecue piezo-igniters. Rub two crystals of quartz together in a darkened room and see an inner glow in the crystals.
35.14.1 Silicates group, polysilicates, polysilicon
About 95% of the Earth's crust consists of silica and silicates. Silicates include the following minerals:
1. Olivine, Peridote, Chrysolite, (Mg Fe)2SiO4
1.1 Olivines, Mg2SiO4
2. 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
Polysilicates are both minerals and manufactured polymers in the form of sheets of the silicate group (SiO4)2-, that are used in ceramics industries and the building industry. Polysilicon forms as chemical vapour deposits and is used in the semiconductor industry for the manufacture of metal-oxide silicon semiconductor transistors.
35.14.2 Opals, SiO2.nH2O
See diagram 6.14.1
Lightning Ridge Opal Mines are most famous sources of opal in Australia.
Opal is similar to chalcedony, but it is a hydrous silica. It has non-metallic lustre, white streak, not good cleavage, conchoidal fracture, white colour, vitreous lustre with colour patches, specific gravity about 2, can scratch glass and be scratched by quartz. This mineral has no definite atomic structure and never occurs as crystals. Opal colour is not formed from impurities or chemicals within the gemstone. Opal has the same chemical structure as glass, SiO2.nH2O. However the molecular structure is different and this difference causes the colour. The opal molecules form in a regular symmetrical pattern. White light enters the opal, and the molecules act as myriads of prisms, and the light is consequently refracted out as various colours. Opal is the product of decomposition of many different rocks and may occur in ore veins and be deposited at hot springs.
1. Solid light (white) opal occurs as two types, milky and crystal. Milky opal is opaque, with the colours visible on the surface only. Crystal opal is transparent with the colours being visible from within the depths of the stone.
2. Opal triplets consist of thin slices of opal affixed to a background of black glass. A dome of clear quartz crystal is then glued to the upper surface. The opal slice is so thin that it becomes totally transparent. Thus, the black background causes the colours to darken dramatically. The crystal dome is to protect and magnify the opal.
3. Opal doublets are similar in construction to triplets, but without the crystal dome. Thus, a slice of opal is glued to a piece of black glass (or similar substance) and the actual opal is then polished. The opal is generally thicker than a triplet, with better quality opal so doublets are more valuable.
4 Dark (black) opals have dark colours, similar to doublets and triplets. Here, however, the dark background is a natural phenomenon. Thus, a black opal is, in fact, a natural doublet with a band of colour sitting on a dark background. Black opals are very rare, so very valuable.
5. Boulder opals are mined in Queensland, Australia, where ironstone boulders occur with thin veinlets of opal running through them. The stones are cut as natural doublets, with part of the seam of opal as the face, and the ironstone as the natural backing. Boulder opals have a similar appearance to black opals, but have less value.
6. Boulder opal matrix is used when the ironstone / opal amalgam is such that full boulder opals cannot be cut. So the fine veinlets and dark ironstone are polished together.
7. Andamooka matrix consists of a mixture of opal and porous rock, and is white in colour. A regular stone is cut from this amalgam and placed in a sugar solution that soaks into the rock. sulfuric acid is then applied to carbonize the sugar and turn it black. Thus, the fine slivers of opal now have a black background to give the finished article the appearance of a black opal.
8. Synthetic opals were developed in France several years ago and are virtually never sold in Australia by virtue of the fact that they are synthetic and have little acceptance.
Australia provides the world with 95% of all precious opal. There are eight varieties of opal available in Australia. Before contemplating the purchase of an opal, it is important to understand each type and the principles of their valuation.
35.14.2.1 Opal valuation
The three basic criteria of evaluation for all opals, light or dark in colour
1. Colour
The more red visible in an opal, the more valuable. The colour hierarchy is red, orange, green, blue.
2. Brightness
Brightness is most important aspect of opal valuation. The brighter and stronger the colour, the better the quality. Thus a bright green stone can be more valuable than a dull red one.
3. Patterns
The larger the splashes of colour, the better the quality. "Pinfire" or "sheen" patterns are the least valuable. The ultimate pattern is the extremely rare and valuable "harlequin" with a symmetrical square checkerboard appearance.
4. Misconceptions
1. Opal is not soft. It has the same hardness as glass.
2. Opal is not unlucky. This was a rumour started about the year 1900 by London diamond merchants to try to protect their then monopoly. For centuries before that, opal had been considered a stone of good fortune.
3. Opal does not shrink in settings.
4. Opal does not lose its colour in the sun or snow (or anywhere).
5. Opal is not affected by water. However in the past, triplets have been glued with a resin that does not agree with moisture. This resin has come apart, causing the opal to appear cloudy. Most triplets now have a water resistant glue so check this before purchasing, and always obtain a guarantee.
35.14.3 Amethyst
A violet-blue variety of quartz. (Greek: amethustos, 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 silica mineral moganite. Chalcedony may be in the form of the following gemstones: Agate, Aventurine, Bloodstone, Carnelian (cornelian), 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. Carnelian is red due to iron impurities. Thunder eggs are in the form of a rock shell filled with agate. Bloodstone occurs as an opaque or translucent mineral, bright or dark green in colour and interspersed with small red spots.
35.21.0 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.
35.21.01 Igneous intrusions, batholith, dyke, sill
See diagram 35.21.01: Igneous intrusions
Molten material from within the earth may reach the surface as a lava flow or force the layers or rock aside to form a massive batholith. Also molten material may move vertically to cut overlying layers as a dyke, usually about three metres wide, or move horizontally between layers to form a sheet-like sill.
35.21.1 Basalt
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
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
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
See 9.226: Teeth and toothpaste
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
Pumice is a volcanic glass pyroclastic lava with high silica content that cooled while still containing large quantities of gases making it light and spongy. 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 can float and are often washed up on beaches and called pumice stones. 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
 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 volcanic bombs large enough to be used for decoration in gardens. Other wise is is used as a base in gas-fired barbecues 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
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.
35.21.5.1 Obsidian
 Obsidian, volcanic glass, is an amorphous solid 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.
35.21.5.2 Porphry
 Porphyry, rock with large isolated crystals of feldspar or quartz surrounded by finer feldspar crystals. "Imperial porphyry" was the purple rock containing large crystals of plagioclase feldspar used for grand buildings in Imperial Rome.
35.21.6 Serpentine
 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. Some geologists say that when serpentine is newly dug out of surrounding rocks and moistened,  it has a characteristic smell.
35.21.7 Tuff
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.
35.21.8 Classify igneous rocks in hand specimens
After Al Grenfell The Australian Science Teachers Journal Vol. 32 No. 3
See diagram 6.21.1a | See diagram 6.21.1b
Use a magnifying glass to classify magmatic rocks by texture and mineralogy. Volcanic types and plutonic types of igneous rocks have cooled and solidified at different rates typically in different physical environments giving different textures. Plutonic rocks are the granites, some porphyries and other igneous unstratified crystalline rocks thought to have formed at great depth and pressure in the earth.
Plutonic rocks have individual grains coarse enough to be individually identifiable usually >1 mm diameter.
Volcanic rocks have no visible crystals
Classify plutonic rocks using the modification of the IUGS (International Union of Geological Sciences) classification of plutonic rocks. Use the triangular coordinate system in diagram 35.21.1a. Use diagram 35.21.1b to estimate the volumetric abundance of the major rock forming minerals.
Divide the surface and sub volcanic magma systems of volcanic rocks into two broad categories with differing flows of energy and modes of eruption.
The magmas are:
1. blown out as pieces of ejecta or
2. erupted or intruded as coherent units.
So you can distinguish corresponding hand specimens on the presence or absence of volcaniclastic texture.
Table 1. shows the chief types of pyroclastic rocks.
Table 2. shows classification of non-fragmented volcanic rocks, e.g. aphyric lava by colour.
Table 3. shows classification of porphyritic volcanic rocks by phenocryst assemblages. Each table can be expanded to accommodate additional volcanic rocks that may be relatively uncommon generally but locally abundant.
Classify igneous rock hand specimens
1a Fine-grained < l. mm aphanitic, (Volcanic rocks)
1b Average grain diameters > 1 mm phaneritic, (Plutonic rocks), Go to 5a 5b
2a Pyroclasts present, (Pyroclastic rocks), See Table 1
2b Pyroclasts absent, grains interlocked, (Non-fragmental volcanic rocks)
3a Ground mass glassy, (Obsidian, volcanic glass, amorphous solid)
3b Ground mass crystalline
4a Aphyric phenocrysts absent, (Aphyric lava), See Table 2
4b Porphyritic phenocrysts present, (Porphyritic volcanics), See Table 3
5a Medium to coarse grained, (Plutonic rocks)
5b Pegmatite (>30 mm), (Pegmatite)
Table 1. Pyroclastic rock types
Rock type: Features
Agglomerate (Pyroclasts >32 mm blocks and bombs rounded pyroclasts predominant)
Volcanic breccia (Pyroclasts >32 mm blocks and bombs; angular pyroclasts predominant)
Lapilli tuff (Pyroclasts 4 to 32 mm and of any shape)
Tuff (Pyroclasts < 4 mm and of any shape)
Ignimbrite (Welded tuff with unsorted nature > 50% fragments < 4 mm pumice clasts common often flattened and with frayed terminations)
Table 2.
Aphyric lava
Rock type (colour)
Mafic lava (dark coloured)
Felsic lava (light coloured)
Table 3.
Porphyritic volcanic rocks
Rock type: phenocryst mineralogy (Plutonic equivalent)
Basalt: +- olivine +-
 +- plagioclase (Gabbro)
Andesite: plagioclase +- mafic phases (Diorite)
Dacite: plagioclase +- quartz + mafic phases (Tonalite)
Rhyodacite: plagioclase + alkaline feldspar + quartz +- mafic phases (Granodiorite)
Rhyolite: alkali feldspar +- quartz +- mafic phases (Granite)
Trachyte: alkali feldspar + mafic phases (Syenite)
35.22  Sedimentary rocks
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
 Sandstone is made up of grains of quartz, SiO2, 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. Quartzite is an altered and exceedingly hard sandstone. Use a magnifying glass to examine the sandstone in any sandstone buildings or walls in your area.
35.22.2  Breccia
 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 Breccia
 Breccia, 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 and in 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, CaSO4.2H2O.
35.22.4.0 Clay
Clay minerals are hydrous aluminium phyllosilicates, tetrahedral sheets of  (Al,Si)3O4, include chlorites, illites, kaolins, and smectites. China clay, white clay is composed of kaolin. Pipe clay is fine white clay formerly used for tobacco pipes, pottery and leather whitening. 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.  Bole is a non-plastic clay that contains iron oxide giving it a yellow to brown colour.
Commercial
1. Modelling clay, "Plasticine"
2. Feeneys clay, based on stoneware clays with refractory grog (mainly silica and alumina) and crushed trachyte, firing range 1000oC to 1280oC, biscuit (bisque) 1020oC minimum
3. Feeneys clay, excellent plasticity, good throwing properties, fires terracotta red at mid fire in oxidation, glazes up to 1200oC, not for reduction or high stoneware temperatures
4. Feeeneys clay, throw, hand build, slab, coil, white / cream earthenware, grey / beige cream stoneware, texture medium, firing range 1000oC to 1280oC,
5. Feeeneys clay, very plastic,  hand building, coiling, throwing on a wheel, texture medium,  firing range 1000oC to 1280oC, general purpose potters clay
6. Blackwattle pottery, paper clay, suitable for air drying and can be fired, decorated and glazed
7. Das, air dry modelling clay, attains hardness without firing, can be coloured
8. Crayola Model Magic, sift and pliable, lightweight and spongy after drying, air dries in 24 hours
35.22.4.01 Chemical weathering reactions
Some weathering reactions need water and some need acid to produce aluminium silicate clays.. Both types of reactions reduces the size of mineral particles with the exclusion of silicic acid.
1. Al2(OH)4(Si2O5) + 5H2O --> 2Al(OH)3 + 2H4SiO4
kaolinite + water --> gibbsite + silicic acid
2. Al2(OH)4(Si2O5) + 6H+ --> 2Al3+ + 2H4SiO4 + H2O
kaolinite + acid --> aluminium ion + silicic acid + water
3. 2KAl2(OH)2(Si3AlO10) + 3H2O + 2H+ --> 3Al2(OH)4(Si2O5) +2K+
muscovite + water + acid --> kaolinite + potassium ion
4. 2KAlSi3O8 + 9H2O + 2H+--> Al2(OH)4(Si2O5) + 2K+ + 4H4SiO4
feldspar + water + acid --> kaolinite + potassium ion + silicic acid
5. Al2(OH)2(Si2O5)2 + 5H2O --> Al2(OH)4(Si2O5) + 2H4SiO4
montmorillonite + water --> kaolinite + silicic acid
6. 2KAlSi3O8 + 12H2O + 2H+ --> KAl2(OH)2(Si3AlO10) +2K+ + 6H4SiO4
feldspar = water + acid --> muscovite + potassium ion + silicic acid
7. 2KAl2(OH)2(Si3AlO10) + 9H2O +2H+ --> 3Al(OH)3 + K+ + 3H4SiO4
muscovite + water + acid --> gibbsite + silicic acid
8. 2Al(OH)3 + 3H+ --> Al3+ + H2O
gibbsite + acid --> aluminium ion + water
Clay minerals include the following groups:
35.22.4.3 Montmorillonite, smectite
Montmorillonite (smectite), (Al,Mg)[(OH2)Si4O10].(Na.Ca)x.4H2O, (Na,Ca)(Al, Mg)6(Si4O10)3(OH)6.nH2O, forms from volcanic ash and occurs in Fuller's earth and bentonite, Al2Mg(OH)2[Si4O10](Ca,Na)x.4H2O. These minerals easily exchange cations and take up and lose water, so are called "swelling clays".
35.22.4.4 Bentonite
Bentonite is often included in products to improve the water holding capacity of soil because of its water absorbing and water retaining properties. Bentonite is a clay-like mineral consisting of hydrous aluminium silicate. It is of very fine grain size, can absorb large amounts of water and has a very high plasticity. It is used in the manufacture of colloidal solutions.
Fuller's earth and bentonite, Al2Mg(OH)2[Si4O10](Ca,Na)x.4H2O. These minerals easily exchange cations and take up and lose water, so are called "swelling clays".
35.22.4.5 Fuller's earth
Fuller's earth and bentonite, Al2Mg(OH)2[Si4O10](Ca,Na)x.4H2O. These minerals easily exchange cations and take up and lose water, so are called "swelling clays". Fuller's earth, a hydrated compound of silica and alumina, has a grey brown colour and a smooth greasy feel. It is used as a filtering material to remove the basic colours of vegetable, animal and mineral oils and as a pigment filler. Fuller's earth is a high calcium clay earth, mainly montmorillonite, used to absorbs grease from raw wool, wool relaxant, shrink and unshrink woollen clothing, decolorize, filter, purify oils and greases. Fulling means to clean and thicken cloth by removing impurities.
35.22.4.6 Vermiculite
Vermiculite, granular form, (inert material for chemical spills, cat litter, insulation, packing, potting mix) Irritating to skin and eyes
Vermiculite, Mg2FeAl[(OH)2AlSi2O10Mg((H2O)4], (Mg, Fe, Al)3(Al, Si)4O10(OH)2.4H2O, is used as a potting medium in horticulture and as heat insulating material. 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.
35.22.4.8 Armenian clay
Armenium bole, Bolus amenus, salameniacum, historically a famous red clay used as a medical astringent, book-binding filler and waterproofing agent containing a high proportion of iron oxides and hydrous aluminium silicates
35.22.5 Conglomerate
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 called rock flour or glacial flour. The melting end of a glacier may show a white waterfall containing the glacial 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
Gypsum, CaSO4.2H2O, 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, (satin spar), that break into plates with a glistening or pearly appearance. Rock gypsum contains some lime and sodium chloride. Gypsum, calcium sulfate, has a habit consisting of fibrous, massive, colourless transparent crystals. It is located in ore bodies in the seams, cavities, water courses and crusts in abandoned workings. The associated minerals are rosasite, linarite and dolomite. 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. The lustre is non-metallic, vitreous, also pearly or silky. Anhydrous calcium sulfate occurs as the mineral anhydrite.
35.22.6.1 Alabaster
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, stone dust and carving stones
See 35.31: Tests for limestone
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. Limestone is also a carving stone
Carving stones include the following:
1. "Creastone" that carves like soap but hardens like stone
2. Hebel blocks that are autoclaves aerated concrete
3. Limestone
4. Talc, soapstone, talcstone, steatite, Mg3Si4O10(OH)2, MgSi8O20(OH)4: 35.23.7
5. Vermiculite, Mg2FeAl[(OH)2AlSi2O10Mg((H2O)4]: 35.22.4.6
When using carving stones, ball clay and glaze, a dust mask or respirator must be worn. Dust control is important to avoid dust exposure to students in later classes. Wet cleanup cloths must be washed before being used again.
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
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
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.
35.22.10 Arenaceous rock, arenite
Sedimentary clastic rocks, mostly silica, < 2 mm grain size.
35.22.11 Argillaceous rock
Contains clay minerals, aluminosilicates, and  include claystones, mudstones, siltstones and shales, supposed to smell like rain on hot ground.
35.23 Metamorphic rocks
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 Classify 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
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 ( Greek: anthrakitēs, glowing coal) is black and shiny.
A coal dust explosion occurs when a concentration of coal dust is lifted and ignited. Ignition of a small quantity of methane gas in a coal mine generates a pressure wave that can lift coal dust and ignites it. Unless the reaction is limited, the coal dust will continue to lift and burn and create an even larger pressure wave so that a coal dust explosion occurs throughout the coal mine. Such explosions can be prevented in two ways
1. Eliminate both ignition sources for methane from electrical equipment or frictional sparking and eliminate accumulations of methane by ventilation.
2. Preventing accumulation of fine coal dust and make inert coal dust accumulations by stone dusting, i.e. application of finely crushed limestone, called stone dust, to make the fine coal dust incombustible. Also, by storing stone dust as passive explosion barriers, any explosion causes dispersal of the stone dust to make the airborne dust cloud incombustible.
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.
35.23.1.1 Coal seam gas, CSG, and coal to liquid, CTL, projects
1. Industry development
Recent expansion of interest in coal seam gas and open cut mining in the Surat Basin, Darling Downs, and Liverpool Plains, Queensland, Australia by several large companies has caused great interest in the community.
The proposed mining is open-cut mining, conversion of low grade coal to liquid in a reactor, coal seam gas extraction and gassification on the site. The Commonwealth Department of Sustainability and Environment has released of 300 conditions for 13 coal seam gas projects and a pipeline to Gladstone. These conditions mainly address biodiversity and aquifer issues. Two recently reported incidents of detection of benzene-related compounds near drilling sites from an unknown cause in SE Queensland. Open cut mining requires large amounts of water for dust suppression. Mining coal seam gas, both uses and releases from the seam a great deal of water, most probably very saline and unusable as is. One proposed use of coal seam gas water is dust suppression and coal washing in a new coal mine. Coal seam gas water is currently being used for dust suppression on roads in the region and coal washing.
2. Agriculture
The area of prime agricultural land, strategic cropping land, in Queensland is very small. Recent Queensland Government announcements suggest that such areas might be increased from two to 4% of the total land. The world food crisis with increases in population will make this land very valuable for the future of humanity. Irrigating tree crops or crops with saline water runs the risk of salinizing top soil layers unless an appropriate leaching regime is followed, leaving the possibility of making underlying aquifers more saline from the leachate. Soils where the lower horizons contain salt, or where the pH is not conducive to plant growth, are very difficult to rehabilitate once disturbed for mining operations.
Remediating salt-affected land is very difficult and requires a long time, enough water to leach salts and saline tolerant plants. The management aim would be to not allow land to become salinized.
Properly treated water can be a very valuable source of irrigation water provided the price to the user is properly negotiated. However, even irrigation with “clean” water carries a landscape salinity risk in our semi-arid environments. Drilling wells in cropping land can disrupt sophisticated controlled traffic operations developed by very skilful farmers to harness the water resources very efficiently and reduce soil compaction. A well in a central pivot irrigation system will disrupt irrigation. It is not clear how much land will be disturbed to build pipes collecting gas from wells.
Coal seam gas wells can be placed in groups on less valuable land for agriculture and "bent" to reach the seam so that they do not disrupt farming operations. A proposed open cut mine for open cut mining would use very poor quality coal leaving large amounts of solid waste residues with ash content about 35% and carbon dioxide to dispose off 10,000 tonnes / day vented into the atmosphere. The mining operation and petrochemical plant would require a great deal of water, 8000 ML / year, equivalent to the amount used by Toowoomba. If this water came from aquifers, it would compete with water currently used for irrigation and town water supplies and draw down these aquifers from which extraction is
regulated.
3. Water
The water use and management by the mining operations could jeopardize the Great Artesian Basin by affecting the pressure and volume of water contained (water level at the bores) and cross contamination from other aquifers. Extracting coal seam gas water from the coal seam may result in movement of water from overlying aquifers into the seam and by that reducing their water levels and the existing use for irrigation. Evaporation ponds filled with coal seam gas water run the risk of contaminating aquifers below with salt and the salt or brine from the ponds needs to be disposed of safely and prevented from contaminating other land in a flood event. However construction standards for evaporation ponds have been substantially improved. They must now be lined and have leak detection systems. Reinjecting the original aquifer with the saline coal seam gas water may be an option but water must be held for the period that gas is being extracted. Reverse osmosis can treat the saline coal seam gas water to a standard suitable for irrigation and household use but leaves a very saline residue to be disposed of. The desalination operation requires a large amount of electrical energy. Green algae and blue green algae can probably be grown for biofuel production in ponds of coal seam gas water containing some salt. However good quality water is likely to be needed to reduce the electrical conductivity of the water to a suitable level and to top up ponds and prevent concentration of salt as water is lost by evaporation. The quality of coal seam gas water and water associated with gassification in situ needs to be continually monitored for toxic organic compounds released from the coal seam. Roads, wells and pipelines associated with the mining in the Condamine River alluvial flood plain run the risk of negating flood control measures recently instigated with community support.
4. Management Issues
Drilling through aquifers to the coal seam runs the risk of allowing cross contamination between aquifers, contaminating sweet water aquifers with salt and possibly methane and other inflammable gases, as has occurred in the USA, making the aquifers unusable. Fracking, (hydraulic fracturing) underground explosions to increase the permeability of rock and coal to gas, runs the risk of contaminating adjacent aquifers and creating or releasing toxic organic compounds. Communities need to be consulted and a consensus reached about access to their properties and where the infrastructure should be placed. New land access arrangements have been recently legislated for. Appropriate soil management is critical for mined land rehabilitation. Native ecosystems and pasture have been successfully established after mining on a range of soil types but rehabilitation of prime agricultural land on vertosols, 35-70%, clay after mining has not happened in Australia or anywhere else in the world. Gassification of coal in situ has considerable risks of contaminating aquifers with toxic, carcinogenic chemicals produced as a by-product or released from the coal seam. Research in Australia has not shown that this can be achieved safely. Also, there is a risk of subsidence. A coal mine plans to expand its open cut mine activities, destroying a town which once was home to 400 people, alienating 2900 ha of prime agricultural land and drawing down the aquifer reserves for a distance of 5 km from the project site of 7,347 ha which would impact on a very large area of agricultural land around the site. Government and industry must proceed cautiously and conduct the necessary research to resolve the issues listed above before any production processes are instigated.
35.23.2 Graphite, diamond, C
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.
35.23.2.1 Amber, C12H20O, Succinite
(Arabic: anbar ambergris) Fossil residue in sedimentary rocks, colourless to apple green to brown, greasy lustre, transparent to translucent, hardness 2-2.5, relative density 1.0 to 1.1, conchoidal fracture, brittle, produces electrostatic charge when rubbed, amorphous non-crystalline, in gravel.
35.23.3 Marble
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
Petroleum consists of crude oil and gas. Crude oil is mostly hydrocarbons with some oxygen, nitrogen and sulphur. The latter may increase the expense of refining. Most scientists think petroleum was formed from the decomposition, heating and burial of organic matter at great depths often of marine organisms. However 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.
35.23.4.1 Oil shale and fracking, (hydraulic fracturing)
Oil shale is a fine-grained shale that yield oil when distilled. Petroleum may be extracted directly from loose shales. However, more petroleum can be extracted if if the shale can be made looser artificially by a process called fracking. Hydraulic fracking fluids can be injected under great pressure along with sand grains or other material to keep the shale particles apart when the hydraulic fluid is removed. However the hydraulic fluids pose a danger of environment pollution if they are forced by pressure to the surface.
35.23.5 Quartzite
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.
Citrine, SiO2, yellow, colour variety of quartz, vitreous greasy lustre, hardness 7, relative density 3, translucent, conchoidal fracture
35.23.6 Slate
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, soapstone, talcstone, steatite, French chalk, Mg3Si4O10(OH)2, MgSi8O20(OH)4
Talc has green to yellow to white colour, hardness 1, white streak, pearly to greasy lustre with a silvery sheen, good but not visible cleavage, occurring in plates or granular form, 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, a filler in glazing and in cosmetics 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 igneous rocks
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 Make 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 Make metamorphic rocks
Fire a shaped piece of clay that has first been dried and put on a piece of broken pottery. Heat the shaped clay in a large crucible over a Bunsen burner.
35.27 Folds
See diagram 35.27: Folds | See diagram 5.27: Folds (Not labelled)
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 | See diagram 5.29: Faults (Not labelled)
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.
35.33.1 Pyroelectricity, ferroelectricity
Some piezoelectric crystals, e.g. tourmaline, are also pyroelectric, i.e. electricity is generated when the crystal is heated and opposite charges gather on the opposite faces of asymmetric crystals. So the heated crystals generate electricity.
Other substances are pyroelectric but are termed ferroelectric because the the direction of charge changes if external electric fields are applied, e.g. gallium nitrate (GaN) and lithium tantalate (LiTaO3).
35.33.2 Dimorphism, aragonite
Aragonite and calcite are the two polymorphs of calcium carbonate, CaCO3. Aragonite has orthorhombic crystals with repeated twinning in "pseudo-hexagonal form", i.e. the angle is 63o48' instead of 65o, to form flower-like aggregates, "flos-ferri", flowers of iron. The carbonates of cadmium, iron, magnesium, manganese, zinc, and the double carbonates of calcium and magnesium are isomorphous with calcite. However the carbonates of barium, lead, and strontium are isomorphous with aragonite. Sodium nitrate crystals are isomorphous with calcite but potassium nitrate crystals are isomorphous with aragonite at room temperature but changes to the calcite form at high temperature. Aragonite forms in the shells of molluscs and freshwater corals. Fossil coral shells, ammolite, is an iridescent gemstone.
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.
35.34.1 Dendrites, false fossils
Manganese and iron oxides and hydroxides may form deposits branching through limestone, dendrites. These branches may be mistaken for fossils, but they are only chemical in origin.
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.
35.40.1 Mapping contours, geological structures, erosion
After N.E. Austin The Australian Science Teachers Journal Vol. 33 No. 1
See diagram 335.9.1
1. Show relief on the map with contour lines. To develop skills in contour line interpretation by experimental means use landform models of the three fundamental surface forms: planar concave and convex. They exist in five spatial forms as in figure 1.
A. Make the five forms A to E from flexible white cardboard. Contour lines are lines joining places of equal altitude i.e. for small regions of the Earth's surface the intersection of equally spaced horizontal planes with the Earth's surface. For landform modelling you can produce such planes with plastic sheets held vertically or 35 mm slides e.g. S1 and S2 as in figure 2 with the back light or projector projecting horizontally.
2. Project S1 horizontally on the five spatial surface forms A to E then look vertically down on to the models. You can vary the inclination of each of the models A to E from 10o to 90o. Also you can vary the concavity or convexity of models B to E if the white cardboard used to make them is flexible. The figure 3 shows what you see when looking vertically down using S1. In A B and C contour lines are straight lines on all surfaces that can be generated by the translation in space of any horizontal straight line moving parallel to itself. In D and E contour lines are curved on all surfaces that can be generated by translation in space of any straight line inclined to the horizontal moving parallel to itself along a curved path.
3. Figure 4 shows what you see when looking vertically down using S2. In A B and C contour line spacing decreases with increasing steepness of the landform. Figure 3D and figure 4D show that if contour lines are concave when viewed from the direction of low altitude to high latitude the landform is concave. Figure 3E and figure 4E show if contour fines are convex when viewed from the direction of low altitude to high altitude the landform is convex. The same spatial forms described above can be used in developing concepts of outcrop in relation to geological structures as in figure 35. In these experiments the projector can be positioned to take into account varying orientations of geological structure and landform.
35.40.2 Isostasy models
After N.E. Austin The Australian Science Teachers Journal Vol. 32 No. 3
See diagram 335.9.2
1. Make a tank from acrylic or glass sheet. Keep a clearance of 2 mm at the sides and ends of the tank. Make a water inlet at the base of the tank to helps filling and draining with a garden hose. Adjust the mass of wooden blocks of various lengths by inserting rolled lead sheet and float the blocks in a water tank e.g. use 50 mm x 25 mm redwood timber density 0.6 g cm-3. Cut a basic length 38 cm long. Calculate its true volume, V. Multiply this volume by 0.7 to find its adjusted mass M. Drill a 9 mm hole centrally upward through the base. Cut a short length of 9 mm dowel to act as a sealing plug in this hole. Put rolled sheet lead in the hole to adjust the relative density to 0.7. Put on a balance the 38 cm block the prepared plug and the rolled lead sheet necessary to bring the total mass up to the calculated adjusted mass. Use lead shot in the final mass adjustment. Insert the prepared lead in the prepared hole after rolling the sheet to fit. Glue in the prepared plug.
2. To make an Airy's model cut 15 lengths of the redwood timber between 38 and 19 cm long. Drill and prepare plugs as above. Calculate the adjusted mass M for each length as above or use formula: Ma LM / 38 where L length in centimetres M mass of density adjusted 38 cm basic length in grams. Adjust all lengths as before. Check all lengths in a one litre measuring cylinder of water by flotation.
3. To make a Pratt's model cut the same number of lengths are cut as before. The shortest possible length now is 28 cm so cut the lengths cut are between 38 and 28 cm. Prepare all drilled lengths and plugs. Use a longer drill hole for short lengths because you must adjust all lengths to the same mass M of the basic adjusted 38 cm. The shorter the length the greater the relative density.
4. To make an erosion block cut a 38 cm length of 100 mm x 50 mm timber. Cut away the top corners of this block using a fine saw. Join the off cuts back together using an aluminium plate. Replace this block in its original position and drill the plate and whole block for a suitable locating pin. Adjust this whole block to a relative density of 0.7 as above. Introduce the larger erosion block into the Airy model. Remove the four shortest blocks from this set and introduce this block near the centre of the array. Remove the cut away upper corner block to simulate erosion and observe the isostatic readjustment. Replace this cutaway to simulating snowfalls and observe the isostatic readjustment.