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Identifying Minerals

Identifying Minerals. 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. Color.

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Identifying Minerals

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  1. Identifying Minerals

  2. 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

  3. 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

  4. Jasper • Has traces of iron oxides giving it a red tinge

  5. Amethyst • Contains ferric iron making it purple

  6. Citrine • Contains iron hydrates making them orange

  7. Rose Quartz • Contains manganese or titanium • Color is the most obvious characteristic of a mineral but it is also the least reliable.

  8. 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

  9. Texture • How a mineral feels to the touch • Smooth • Rough • Ragged • Greasy • Soapy • Glassy • Texture test is perhaps the most subjective

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. Ores and Gems

  17. Ores • A useful mineral can be mined for a profit • Examples • Hematite – source of iron • Bauxite – source of aluminum • Rutile – source of titanium

  18. 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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