School Science Lessons
Earth and space sciences
2009-08-29
Please send comments to: J.Elfick@uq.edu.au
Geology
See: Chemistry index and minerals, alphabetical list of terms
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
35.3.1 Minerals mined at the Broken Hill mines
35.3.1.1 Silver, Ag
35.3.1.2 Lead, Pb
35.3.1.3 Zinc, Zn
Ore minerals of the primary (sulfide) zone
35.3.2.1 Galena (lead sulfide, PbS
35.3.2.2 Sphalerite (zinc sulfide, ZnS)
Gangue (waste) minerals of the primary (sulfide) zone
35.3.3.1 Bustamite, calcium manganese silicate, MnCaSiO6
35.3.3.2 Rhodonite, manganese silicate ([Mn, Ca]SiO3)
35.3.3.3 Garnet (spessartine) manganese aluminium silicate (Mn3Al2Si3O12)
Other minerals of the primary (sulfide) zone
35.3.35.1 Chalcopyrite, copper iron sulfide
35.3.35.2 Pyrite, iron sulfide
35.3.35.3 Pyrrhotite, iron sulfide
35.3.35.4 Rhodochrosite, manganese carbonate, MnCO3
Ore minerals of the oxidized zone
35.3.35.5 Anglesite, lead sulfate, PbSO4
35.3.35.6 Azurite (copper carbonate)
35.3.35.7 Cerussite, lead carbonate, PbCO3
35.3.35.8 Copper
35.3.35.9 Coronadite (lead manganese oxide)
35.3.35.10 Goethite, FeO(OH), hydrated iron oxide, hydrous iron oxide
35.3.35.11 Gypsum, calcium sulfate
35.3.35.12 Malachite, copper carbonate
35.3.35.13 Pyromorphite, Pb5(PO4)3Cl
35.3.35.14 Silver, Ag
35.3.35.15 Smithsonite, zinc carbonate, ZnCO3
35.12.1 Touchstone
35.14.2 Opals
35.14.3 Amethyst
35.14.4 Chalcedony
35.21.8 Classify igneous rocks in hand specimens
35.23 Metamorphic rocks
35.23.01 Classification of metamorphic rocks
35.23.1 Coal, coal dust explosions
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
35.24 Make artificial igneous rocks, alum crystals, sulfur crystals
35.25 Making artificial rocks, sedimentary rocks
35.26 Making artificial rocks, metamorphic rocks
35.27 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
35.40.1 Mapping contours, geological structures, erosion
35.40.2 Isostasy models
35.3.1 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.
The main metals mined for at Broken Hill are as follows:
35.3.1.1 Silver, Ag, occurs in a variety of minerals but most of the silver is found as trace amounts of silver mineral locked up inside the lead mineral, galena. Sometimes silver occurs as big lumps, nuggets, of the metal itself. Only silver ever comes out of the ground as a metal. Lead and zinc are always locked away minerals, as is most of the silver. Silver is largely used in the photographic industry although it has uses in jewellery, electronics and silverware.
35.3.1.2 Lead, Pb, occurs mainly as the lead ore galena (lead sulfide, PbS) It is characterized by a metallic silver lustre and cubic fracture. Cerussite (lead carbonate, PbC03) and anglesite (lead sulfate, PbSO4) are found in areas where galena has been weathered or exposed to oxidizing groundwater. Typically this occurred at or near the surface. Lead was used in water pipes, roofing and pigments but is now mostly used in batteries for vehicles and other equipment.
35.3.1.3 Zinc, Zn, occurs mainly as sphalerite (zinc sulfide, ZnS). At Broken Hill it has a black resinous appearance but rarely shows as big crystals. Smithsonite (zinc carbonate, ZnCO3), resulting from the weathering and oxidation of ore by groundwater, is found in areas where the ore body was at or near the surface. Zinc is used in galvanized coatings of iron and steel. It is also used in die cast alloy products, pigments and other industrial and agricultural applications.
Ore minerals of the primary (sulfide) zone
35.3.2.1 Galena (lead sulfide, PbS is the main lead ore mineral at Broken Hill. The silvery metallic lustre and cubic appearance characterize galena. It has a relative density of 7.35. Galena is also the source of much of the silver at Broken Hill. Silver atoms can substitute for lead atoms or be present within minerals such as acanthite (Ag2S) that have formed within the galena.
35.3.2.2 Sphalerite (zinc sulfide, ZnS) is the main zinc ore mineral at Broken Hill. Good crystalline sphalerite is unusual at Broken Hill. The colour of sphalerite varies with its impurities. At Broken Hill it is black but some rare large crystals have a deep red colour.
Gangue (waste) minerals of the primary (sulfide) zone
35.3.3.1 Bustamite, calcium manganese silicate, MnCaSiO6, also occurs in the galena-rich lodes. It has a range of pink to orange to deep brown colours.
35.3.3.2 Rhodonite, manganese silicate ([Mn, Ca]SiO3) is the most abundant manganese mineral found in the galena-rich ore bodies. It has a range of beautiful red-pink colours.
35.3.3.3 Garnet (spessartine) manganese aluminium silicate (Mn3Al2Si3O12, is a port wine red mineral commonly associated with galena ore.
Other minerals of the primary (sulfide) zone
35.3.35.1 Chalcopyrite, copper iron sulfide, occurs in veins in garnet, quartzite and garnet sandstone in ore bodies. The associated minerals are argentiferous galena and arsenopyrite.
35.3.35.2 Pyrite, iron sulfide, is found in lining cavities in faults and fractures in ore bodies. The associated minerals are calcite and rhodocrosite.
35.3.35.3 Pyrrhotite, iron sulfide, is found in veins, zones and bands in ore bodies. It can be weakly magnetic but not at Broken Hill. The associated minerals are calcite, galena, and chalcopyrite.
35.3.35.4 Rhodochrosite, manganese carbonate, MnCO3 is a pink mineral found in fault zones along with other carbonate minerals, e.g. calcite.
Ore minerals of the oxidized zone
35.3.35.5 Anglesite, lead sulfate, PbSO4, is another widespread secondary mineral from the oxidized zones of the mine. It is found in vughs (irregular voids) and fractures in all mines in the outcrop area. The associated minerals are marshite, iodargyrite, pyromorphite, stalactitic goethite, and goethite matrix replaced by cerussite.
35.3.35.6 Azurite (copper carbonate) has a habit consisting of short tabular prisms, equidimensional plates, long spear-like crystals with pyramidal terminations. The associated mineral is malachite.
35.3.35.7 Cerussite, lead carbonate, PbCO3, occurs as ore grade concentrations. It is a secondary mineral from the oxidized zones. Most Broken Hill cerussite is opaque white, but wine yellow, yellow brown. smoky brown, transparent and translucent examples are known. It occurs as reticulated masses, complex arrowheads “twinned crystals”, and "jack straw" masses of tubular-shaped crystals. It is found in ore bodies and is one of the most abundant minerals of the oxidized zone. The associated minerals are malachite, azurite, and bromian chlorargyrite.
35.3.35.8 Copper has arborescent forms in large cavities, four-sided wire prisms, elongate octahedrons with repeated branches. Also, stalactitic or dendritic masses in wire-like groups and “nail head” crystals. The associated minerals are cuprite and malachite.
35.3.35.9 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.
35.3.35.10 Goethite, FeO(OH), hydrated iron oxide, hydrous iron oxide, has a habit consisting of botryoidal, mamillary, stalactitic masses and crusts. It is abundant in the gossanous capping of the ore bodies. The associated mineral is coronadite.
35.3.35.11 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.
35.3.35.12 Malachite, copper carbonate has botryoidal and sometimes velvety habit. It is found in ore bodies as powdery to compact fibrous crusts and hemispherical aggregates. The associated minerals are azurite and cerussite.
35.3.35.13 Pyromorphite is the most common lead phosphate, Pb5(PO4)3Cl. It is a secondary mineral from the oxidized zone. It has a large range of habits and colours including coatings and sprays, simple hexagonal prisms, stout hexagonal prisms, branching aggregates, mamillated, botryoidal and colloform masses. It is found all along the lode outcrop. The associated minerals are coronadite, cerussite, secondary galena, and anglesite.
35.3.35.14 Silver has massive, wire habit The associated minerals are gold and copper.
35.3.35.15 Smithsonite, zinc carbonate, ZnCO3, is a widespread secondary mineral from the oxidized zones. It occurs as rounded botryoidal aggregates resembling drops of wax and as honeycombed masses in ore bodies. It is the most abundant secondary carbonate after cerussite. The associated minerals are coronadite and goethite.
35.12.1 Touchstone is a form of schist used to assay gold by comparing the streak of the sample to the streak of "touch needles" with known gold content.
35.14.2 Opals
See diagram 35.14.1
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. The most famous sources of opal are the Lightning Ridge Opal Mines.
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.
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.
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: not intoxicate, amethyst was thought to be a charm against inebriety)
35.14.4 Chalcedony
It is fibrous with very small crystals of quartz and the silca mineral moganite. Chalcedony may be in the form of the following gemstones: Agate, Aventurine, Bloodstone, Carnelian, Chrysoprase, Heliotrope, Jasper, Onyx, Sard
Agate is concentrically banded in crazy patterns it is called agate. Onyx is in flat layers. Sardonyx is in the form of white and brown red bands. Cornelian is red due to iron impurities. Thunder eggs are in the form of a rock shell filled with agate. Bloodstone occurs as an opaque or translucent mineral, bright or dark green in colour and interspersed with small red spots.
35.21.8 Classify igneous rocks in hand specimens
After Al Grenfell The Australian Science Teachers Journal Vol. 32 No. 3
See diagram 5.21.1a | See diagram 5.21.1b
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.
Classification of 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)
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 +- augite +- 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)
35.23 Metamorphic rocks are the result of heat and pressure applied to igneous and sedimentary rocks. The pressure causes mineral grains to align in a single plane so the rock tends to split in this direction. This alignment is called foliation. However, marble and quartzite are metamorphic rocks but are not foliated. Metamorphic rocks are similar to igneous rocks in that they are hard and have interlocked mineral grains. Thermal metamorphism, contact metamorphism, is caused by heat when molten lava heats rocks to form fine grain rocks with no bands or layers, e.g. hornfels. Regional metamorphism refers to the changes caused by extensive heat and pressure to produce coarse grain, banded rocks, e.g. gneiss.
The three varieties of foliation are as follows:
1. Gneissic or banded foliation shows distinct bands of different minerals. The thicker bands are usually feldspar.
2. Schistosis foliation is caused by the parallel arrangement of platy minerals, e.g. mica.
3. Slaty cleavage refers to the tendency of a rock to split into thin, even slabs, e.g. slate.
The cleavage is the result of the parallel planar arrangement of microscopic mineral grains.
35.23.01 Classification of metamorphic rocks
1. Foliated, banded or platy:
1.1 Coarsely banded, bands irregular in thickness (gneiss)
1.2 Schistose, regular banding, medium in thickness, and platy (schist)
1.3 Slaty regular fine banding and platy (slate)
2. Non-foliated, massive or granular:
2.1 Mainly calcite or dolomite (marble)
2.2 Mainly quartz - quartzite
2.3 Mainly serpentine and / or talc (serpentine or talc)
2.4 Mainly organic, grey or black (graphite and anthracite coal)
35.23.1 Coal is mainly carbon from woody material, algae and any plant debris that collected millions of years ago in swamps. The heat and pressure caused by overlying deposits of sand and clay caused the formation of coal. The older the coal the greater the percentage of carbon. Peat is a lowest quality coal. It has a high percentage of water. Lignite or brown coal is older than peat and has received much more compression. Bituminous coals are hard, black and brittle. Anthracite is black and shiny.
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.
35.23.2 Graphite, like diamond, consists of the crystallized carbon, C. Graphite has metallic lustre, can mark paper, grey to black colour, black streak, cleavage in one direction, and relative density 2.1. It is soft, black and opaque. It is greasy to touch and leaves a grey dust on the fingers so it is a good lubricant for machinery and "lead" pencils. The softer lead pencils, the "B" grade, contain more graphite in the "lead". By contrast diamond is crystallized carbon but it is one of the hardest minerals and is colourless and transparent. Graphite is a good conductor of electricity but diamond does not conduct electricity. Graphite is also used as stove polish and dry lubricants in the electrical industry. It occurs in crystalline igneous and metamorphic rocks and is also made artificially by heating coke in a furnace. The central electrode of a dry cell battery is made of carbon.
35.23.3 Marble, CaCO3, is a crystalline limestone formed by the heating of limestone rock under pressure, thermal metamorphism. If limestone is heated strongly, it gives off carbon dioxide leaving quick lime, calcium oxide, CaO. If limestone is heated under great pressure it melts and does not lose carbon dioxide. If it then cools slowly, it recrystallizes as marble. Marble is a beautiful building stone, valued for its smoothness and hardness. Pure white marble is recrystallized calcite and looks like a sugar cube. Different colours in marble are caused by impurities, e.g. dolomite, silica, iron, clay minerals. A common method of preparing carbon dioxide is to add hydrochloric acid to marble chips. Not all polished stones are marbles.
35.23.4 Petroleum, crude oil, is a mixture of hydrocarbons often with sulfur and nitrogen. Most scientists think it was formed from the remains of marine organisms buried at great depths, although some people suggest an inorganic origin. Oil deposits usually occur in sedimentary rocks with a thick layer of rock above and below. The oil may float on a layer of water and be under a layer of natural gas, a mixture of gaseous hydrocarbons, mainly methane. Crude oil is usually a dark green, brown or black oily liquid with a characteristic smell. It always occurs with gas and water. A waxy form of petroleum is made from coal.
35.23.5 Quartzite is an altered and exceedingly hard sandstone. The grains have been bound together by a cement formed by the dissolving action of heated water. The constituent grains have been recrystallized to form dense interlocked cementation. When sandstone is broken, only the cement holding the sand grains together is damaged. If a piece of quartzite is shattered, both the sand grains and cement are broken because the particles are so strongly bound together. Quartzite has a glistening appearance caused by its sugar-like crystal structure. Quartzite is white when pure, but most of it contains mica, iron, feldspar or other mineral particles that alter the colour to grey, brown, red, yellow, green or black. Owing to its extreme hardness, quartzite has few commercial uses except road-making.
35.23.6 Slate is a dense rock with a texture so fine that the individual grains in it cannot be seen by the eye or even through a magnifying glass. Slate comes from clay, mudstone and shales altered by heat and pressure. It was once laid down as alluvial material at the bottom of lakes and oceans. Fossils of long dead marine plants and animals can be seen perfectly preserved in it. Most slate is grey, dark grey or black, depending on how much plant material it contains. It may also be green because of the chloride in sea water, or red, purple, yellow or brown because of iron stains. Slate has a well-marked cleavage so the surface of the flat broken piece of slate feels soft and silky. Although easily cut, slate resists the weather so it is for roofs. Formerly, school children learnt their lessons on small slate boards that they could write on with chalk and later erase the writing.
35.23.7 Talc, Mg3Si4O10(OH)2, has green to yellow to white colour, hardness 1, white streak, pearly to greasy lustre with a silvery sheen, good but not visible cleavage, 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 artificial igneous rocks, alum crystals, sulfur crystals
1. Crystallization of alum solutions is similar to the formation of coarse grained and fine grained igneous rocks. Fill a test-tube one quarter full of powdered potash alum, [Al2(SO4)3.K2(SO4).24H2O] [also shown as KAl(SO4)2.12H2O]. Slowly add just enough boiling water to dissolve the alum. Hold the test-tube in a flame so that the mixture boils gently. 1. Pour half the solution into a shallow metal container. Place a piece of string partly in the liquid and add a seed crystal. Stir the alum solution in the container so it cools quickly. 2. Hang another piece of string in the test-tube so that it reaches the bottom and add a seed crystal. Place the test-tube where it will cool slowly. Examine the two solutions the following day and note the sizes of the crystals formed.
2. Melt some sulfur in a test-tube. Fit a filter paper into a funnel and pour the molten sulfur into it. As the sulfur cools it begins to solidify, first forming a crust on the surface. As soon as the crust has formed, remove the filter paper from the funnel and unfold it, so that the still liquid sulfur in the lower part of the filter can flow away from the crust. Note a mass of small crystals on the underside of the crust. Use a magnifying glass to observe the shape of these crystals.
3. Melt sulfur in a test-tube then pour it into a large beaker of water so that it solidifies rapidly to form plastic sulfur. Take it out of the water and examine it after two hours. The solid sulfur formed is very hard and you cannot see crystals with a magnifying glass. However, very tiny crystals may be seen with a microscope.
35.25 Making artificial rocks, sedimentary rocks
1. Use a hammer to grind different coloured sedimentary rocks, keeping the colours separated. Put coloured powdered particles in a glass jar as different layers. Let water trickle down the inside of the jar so as not to disturb the layering until the water is 1 cm above the sediments. Put the jar in the sun and let the water evaporate. Wrap the jar in a thick cloth and break it with a hammer.
2. Mix Portland cement with water and put it in a mould until it hardens. Break the set cement with a hammer and examine the outside and inside surfaces.
3. Mix dry cement with twice as much sand or gravel to form concrete. Add water, mix thoroughly, and place it in a mould. Leave the concrete to harden for several days. Break the set concrete with a hammer and examine the outside and inside surfaces. Note whether the concrete is easier or harder to break than the Portland cement.
4. Mix plaster of Paris with a small amount of water and put it in a mould until it hardens. Stir rapidly or it will harden while being mixed. Break the set plaster with a hammer and examine the outside and inside surfaces. Note whether the plaster is easier or harder to break than the Portland cement or the concrete.
35.26 Making artificial rocks, metamorphic rocks
Fire a shaped piece of clay that has first been dried and put on a piece of broken pottery and heated it in a large crucible over a Bunsen burner.
35.27 Folds
See diagram 35.27: Folds
Folds occur where parallel layer form an arch, anticline, or form a trough, syncline. The line along which the direction of dip changes is the hinge line. Arrange carpets or blankets in layers on the floor. Push the layers horizontally to create anticlines and synclines.
35.28 Joints
Joins are fractures in rocks where no relative movement occurs each side of the fracture. Joints can be caused by cooling shrinkage and increased tension within the rock.
35.29 Faults
See diagram 35.29: Faults
A fault is a fracture in rock where some displacement has occurred. The fault plane of the fracture can be vertical but usually there is a dip of the fault. Dip-slip movement is where the direction of movement on the fault plane, is parallel to the dip of the fault, i.e. up or down. Strike-slip movement is where the direction of movement on the fault plane is parallel to the strike of the fault, i.e. sideways. This movement results in tear faults. The throw of a fault is the vertical displacement between blocks of rock. The heave of a fault is the horizontal displacement of blocks of rock. The hanging wall is the surface with rock above it. The footwall is the surface with rock below it. A normal fault is a dip-slip fault with the hanging wall on the downthrow side, i.e. it appears that a block has slipped down the fault. A reverse fault is a dip-slip fault with the hanging wall on the upthrow side, i.e. it appears that a block has been pushed up the fault. A trough fault is caused by downthrow movement between two parallel faults to form a graben or rift valley. Upthrow between two parallel faults results in a horst. A series of parallel faults is called step faulting.
Make layers of modelling clay, Plasticine. Cut the layers vertically then cut the layers at an angle to create a model of a fault.
35.30 Examine sand with a magnifying glass
The nearly colourless crystals are probably the mineral quartz. Look for other minerals in the sand.
35.30.1 Quicksand
Areas of quicksand have a source of upwards pressure from a spring below. The sand becomes suspended and frictionless so will not support weight on it. A person caught in quicksand should try to float on the back and keep the arms below the surface. The nose and mouth should remain above the surface and allow a slow and laborious paddling to the edge of the quicksand.
35.31 Tests for limestone
Drop lemon juice, or vinegar, or dilute hydrochloric acid on rock specimens. Limestone will effervesce or bubble caused by carbon dioxide gas given off. Marble, a metamorphic rock made from limestone, will also respond to this test.
35.32 Sort sediments
Thoroughly mix equal portions of gravel, coarse sand particles, and clay particles. Place this mixture in a glass jar, not more than half full. Fill the jar with water. Place a cap on the jar and shake vigorously. Allow the material to settle. The components will arrange themselves in order, with the heavier particles at the bottom and the clay particles on the top.
35.33 Piezoelectricity
See 32.1.2: Pressure, piezoelectricity (Electronics)
Piezoelectricity is the phenomenon in certain crystals anc ceramics when application of mechanical stress causes electric charge with the voltage proportional to the stress. It occurs in crystals of cane sugar, quartz, Rochelle salt (potassium sodium tartrate-4-water), topaz, tourmaline,
Demonstrate piezoelectricity by dusting the cooling or warming crystal with a dust of red lead and sulfur that has passed through a silk or nylon screen. A simple bellows can be made from a plastic nasal spray or deodorant bottle in that the aperture has been enlarged to allow a sizeable spray to be emitted. Place in the bottle a mixture of about 2 parts red lead to 1 part sulfur. Put a small piece of silk or nylon stocking over the mouth of the bottle. Tighten this with a rubber band. The dust particles receive electric charges as they pass through the screen formed by the stocking. They settle on the end of the crystal that attracts them. The red lead gets a positive charge and goes to the negative end of the crystal. The sulfur gets a negative charge and settles on the positive end of the crystal.
35.33.1 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.
35.22.4 Clay consists of decomposed weathered rock, usually granite, or others that contain feldspar. Pure clay is a dazzling white, has a soft, oily feel and is easily broken. Damp clay is sticky and has a special smell. It absorbs water and becomes plastic when wet. Clays do not split along bedding planes, i.e. a surface parallel to the original deposition surface. It has particle size less than 0.004 mm diameter, 1/256 mm. Clay minerals can take up or lose water according to temperature and amount of available water. Modelling clay, Plasticine, plastilina, is manufactured for use mainly by children. Bole is a non-plastic clay that contains iron oxide giving it a yellow to brown colour.
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 sliicic 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:
35.22.4.1 Illite, KAl4(Si, Al)8O20(OH)4, KAl4(Si,Al)8O18.2H2O is the most common clay mineral.
35.22.4.2 Kaolinite, Al2(OH)4 (Si2O5), Al4Si4O10(OH)8, weathering product of feldspars, known as white clay, pipe clay, ball clay, Cornish clay and China clay, (also dickite and nacrite minerals) is used in the manufacture of fine porcelain that is almost pure kaolin. The cheaper grades are made with the addition of feldspar. It is a soft white powder, insoluble in water, dilute acids or alkalies. Kaolin clay contains mainly kaolinite and some illite
35.22.4.3 Montmorillonite, smectite (Na, Ca)(Al, Mg)6(Si4O10)3(OH)6.nH2O, forms from volcanic ash and occurs in Fuller's earth and bentonite. These minerals easily exchange cations and take up and lose water, so are called "swelling clays".
35.22.4.4 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 aluminum 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.
35.22.4.5 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.
35.22.4.6 Vermiculite (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.
35.22.4.7 Halloysite, Al4Si4(OH)8O10.4H2O, clay mineral