CLASSIFYING MINERALS While you can classify rocks as pretty or interesting, you can't use those terms when sharing legitimate information about the rock or mineral before you. Here are some good classification categories that will help you both identify and talk about rocks. Most minerals can be identified by their visible properties, although real mineralogists often use microscopy to nail down the details of the mineral. When classifying minerals, look for the color you see, the streak, and the luster first. Color actually doesn't help much because the same mineral can be different colors. In addition, you can have real gold looking a lot like fool's gold, which is iron pyrite. Quartz is purple if it has a bit of iron in it; if not, it will be clear in color. Purple in quartz means it is really called amethyst. Next, check the streak, which is the mineral's powder color. It doesn't vary nearly as much as color so it is a better measure of what the mineral really is. Quartz has no streak; many others don't either. Simply scrape it across any unglazed white porcelain plate. Pyrite, which is gold in color, has a black streak, while real gold has a goldencolored streak. Hematite is black but has a reddish brown streak. Luster is how well the light shines off a mineral. You can also describe it as how metallic it is or non-metallic. Iron-pyrite has a metallic luster as the light shines off it. Quartz is non-metallic. Here are some common lusters and what they really look like in layman's terms: •
Amantadine – sparkly appearance like a diamond
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Earthy – dull or clay-like appearance
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Resinous – looking like tree sap resins such as sulfur
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Pearly – looking like a pearl
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Silky – having long soft fiber-like appearance
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Vitreous – looking like glass or like quartz
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Metallic – looking like a shined or polished metal
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