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IDENTIFYING MINERALS
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Mineral Identification Geologist test physical and chemical properties to identify minerals Color Luster Texture Streak Hardness Cleavage and Fracture Density and Specific Gravity Special Properties
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Color A mineral’s color is a result of chemical composition and presence of trace elements Many minerals can be found in more than one color or shade Example – Quartz can be found in several different forms
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Jasper Has traces of iron oxides giving it a red tinge
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Amethyst Contains ferric iron making it purple
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Citrine Contains iron hydrates making them orange
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Rose Quartz Contains manganese or titanium Color is the most obvious characteristic of a mineral but it is also the least reliable.
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Luster How the surface of a mineral reflects light Two main categories Metallic – mineral shines like chrome Nonmetallic – minerals do not shine More specific type of nonmetallic Dull Pearly Waxy Silky
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Texture How a mineral feels to the touch Smooth Rough Ragged Greasy Soapy Glassy Texture test is perhaps the most subjective
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Streak The color of the mineral in powder form Tested by rubbing the mineral across an unglazed Streak color is not always the same as the mineral color in rock form Example – pyrite is gold in rock form but has a greenish-black streak
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Streak cont. Different variations of a mineral have the same streak Example – Flourite can be purple, yellow, green, or blue but the streak is always white When can this test not be used? When the minerals are harder than a porcelain plate
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Hardness A measure of how easily a mineral can be scratched. Measured on the Moh’s Hardness Scale One of the best identification tests 1-10 scale: Talc is the softest, diamond is the hardest Common objects can be used to measure hardness
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MineralMoh’s Scale Hardness Hardness of Common Object Talc1 (softest) Gypsum2Fingernail (2.5) Calcite3Piece of copper (3.5) Flourite4Iron nail (4.5) Apatite5Glass (5.5) Feldspar6Steel file (6.5) Quartz7Streak plate (7) Topaz8Scratches quartz Corundum9Scratches topaz Diamond10 (Hardest)Scratches all common materials
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Cleavage and Fracture Both describe how a mineral breaks Cleavage – splits easily and evenly along flat planes Mica Fracture – breaks with rough, jagged edges Quartz
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Density and Specific Gravity Density Very good identification tool Mass divided by volume Density is different than weight Consider two different amounts of the same mineral Their weights would be different Their densities would be equal Specific Gravity Ratio of the weight of a substance to the weight of an equal volume of water at 4° C
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Special Properties Some minerals have unique physical and chemical properties Double Refraction – light bends in two directions when it passes through the mineral Magnetism – mineral is naturally magnetic magnetite Odor – sulfide produces a rotten-egg smell when rubbed on streak plate Fizzes – chemical reaction to acid or other solutions Calcite and hydrochloric acid Taste
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ORES AND GEMS
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Ores A useful mineral can be mined for a profit Examples Hematite – source of iron Bauxite – source of aluminum Rutile – source of titanium
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Gems Are nothing more than minerals that are valuable simply because they are prized for their rarity and beauty Examples – Diamonds, Rubies, Amethyst
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