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5.4Mineral Groups Objectives
Describe the properties of the most common minerals (silicates and carbonates). Describe tests used to identify mineral groups.
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Major Silicates 90+% of the minerals in Earth’s crust are members of the silicate family Silicate: a compound of silicon, oxygen, and usually one or more metallic elements Basic building block is the silica tetrahedron Classified by the ways the tetrahedra are linked together
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Quartz Second most abundant mineral in the Earth’s crust
Made entirely of tightly bound silica tetrahedra Chemical name: silicon dioxide 2 oxygen atoms per silicon atom
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Quartz cont’d Looks: Fracture: Hardness: Glassy or greasy luster
Pure quartz = colorless or white Other colors = rose, amethyst (purple), smoky Fracture: Conchoidal or irregular Hardness: 7 on the Mohs scale Common property used to identify it Hardest of the common minerals
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Quartz cont’d Hardness and how it looks:
Make it ideal for certain uses Watch movements Prisms Heat lamps Lenses Glass Paints Jewelry
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Quartz cont’d Found in granite
Important part of many other types of rocks Most sands are made mainly of quartz
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Feldspars Makes up 60% of Earth’s crust Share 3 features
2 directions of cleavage Hardness of 6 Pearly luster Made of aluminum, oxygen, and silicon atoms Creates a net electrical charge Balanced by the addition of other metals Potassium Sodium calcium
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Feldspars cont’d 2 major groups Potassium feldspars
Most common is orthoclase Light-colored pink or salmon 2 cleavage surfaces meet at right angles Most commonly found in granite
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Feldspars cont’d Sodium-calcium feldspars Plagioclase
Albite and labradorite Range in color from white to gray 2 cleavage surfaces meet at slightly less than a right angle One cleavage surface is often marked by fine parallel lines (striations)
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Feldspars cont’d Important rock-forming minerals
Important economically Manufacture of glass and ceramics
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Other Silicates Pyroxene family Occur widely
Cleavage surfaces meet at nearly right angles Common member augite
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Other silicates cont’d
Ferromagnesian silicate Can belong to almost any of the silicate families All contain iron and magnesium Always dark in color Example Augite 2 good cleavages Hardness 5-6
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Other Silicates cont’d
Mica family Soft Hardness = 2.5 Perfect cleavage Form flat crystals that cleave in only one direction Makes thin sheets or flakes Can be easily picked out of rocks Examples Muscovite (white mica) Silvery white Biotite Dark brown or black Used for paints, plastics, rubber, roofing, electronic insulators
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Carbonates Carbonate: a mineral made of negatively charged carbonate ions bonded to positive metal ions 1 carbon atom covalently bonded to 3 oxygen atoms Examples Limestone Marble
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Carbonates cont’d More examples Calcite (calcium carbonate)
Most common carbonate mineral Colorless or white Hardness = 3 Can be scratched with a knife Bubbles with the acid test Dolomite (calcium magnesium carbonate) Occurs as coarse or fine grains in dolomitic limestones Hardness = 3.5-4 Cannot be scratched with a knife Will not react during an acid test
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Oxides and Sulfides Contain significant amounts of iron
Not as common as silicates or carbonates Used to make steel, magnets, car parts, medicines, cosmetics, plastics, and paints
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Oxides and Sulfides Oxide: a mineral made of a metal element combined with oxygen Sulfide: a mineral made of a metal element combined with sulfur
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Hematite Most common iron oxide Usually red Earthy luster
Uneven fracture Some have a silvery metallic luster Gemstones Leave a red-brown streak on a streak plat
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Magnetite Black iron oxide Attracted to magnets Example Lodestone
Natural magnet First compass needles
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Pyrite Iron sulfide Most common sulfide mineral Color
Pale brass to golden yellow Commonly referred to fool’s gold
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5.4 Exit Ticket Describe the properties of the most common minerals (silicates and carbonates). Describe tests used to identify mineral groups.
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