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Indentifying minerals

Indentifying minerals. Mineral identification is based on chemical and physical properties Minerals are identified through: color, luster, texture, streak, hardness, cleavage/fracture, and density/specific gravity. Color. Color is sometimes caused by the trace elements or compounds in minerals

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Indentifying minerals

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  1. Indentifying minerals • Mineral identification is based on chemical and physical properties • Minerals are identified through: color, luster, texture, streak, hardness, cleavage/fracture, and density/specific gravity

  2. Color • Color is sometimes caused by the trace elements or compounds in minerals • Ex. – quartz can be found in a number of colors

  3. Orange citrine – contains iron hydrates

  4. Purple amethyst – contains ferric iron

  5. Red jasper – trace elements of iron oxides

  6. Luster • The way a mineral reflects light is called luster • Luster is described as being either metallic or nonmetallic • Ex. – metallic – gold, copper, and galena have shiny surfaces that reflect light like the chrome trim on cars • Ex. – nonmetallic – calcite, gypsum, sulfur, and quartz do not shine like metals

  7. Texture • Texture describes how minerals feel to the touch – smooth, rough, ragged, greasy, soapy, or glassy • Ex. – fluorite has a smooth texture, while the texture of talc is greasy

  8. Streak • Streak is the color of a mineral when it is broken up and powered • Streak is tested by rubbing a mineral across an unglazed porcelain plate • Sometimes the streak left behind doesn’t match the minerals exterior color Ex. – pyrite (fool’s gold) looks like gold, but leaves a greenish-black streak gold leaves a yellow streak * streak test is one of the main tests used to distinguish pyrite from gold • Minerals streak very rarely changes even if weathered or its external color varies Ex. – fluorite can be purple, yellow, green, or blue, but its streak is always white

  9. Hardness – is a measure of how easily a mineral can be scratched - German geologist developed a scale in which an unknown mineral’s hardness can be compared to known hardness of ten minerals

  10. Cleavage and fracture • Atomic arrangement also determines how a mineral will break • Minerals break along planes where atomic bonding is weak • Cleavage – when a mineral splits relatively easily and evenly along one or more flat planes • Fracture – minerals that break with rough or jagged edges

  11. Density and specific gravity • Sometimes two minerals of same size may feel quite different when lifted due to their densities • Density reflects atomic weight and structure of mineral – thus it is very helpful in identification because it is not based size or shape of mineral • At times densities are too close to distinguish by lifting only – specific gravity, ratio of weight of substance to weight of equal volume of water

  12. Special properties • Double Refraction – bending of light in two directions (Iceland spar) • Some elements fizz – calcite fizzes when it comes in contact with hydrochloric acid • Some have magnetic properties (lodestone) • Some produce a rotten-egg smell when rubbed across a streak plate (sphalerite)

  13. Mineral uses • Minerals are used in almost everything – computers, cars, televisions, desks, roads, buildings, jewelry, beds, paints, sports equipment, and medicines

  14. Ores • Any mineral that contains useful substances that can be mined for a profit is called an ore • Ex. – hematite is an ore that contains iron (any item you see made of iron was orginally hematite) • Ex. – bauxite is an ore that contains aluminum

  15. hematite iron

  16. bauxite Aluminum

  17. Mines • Ores are located deep in the Earth’s surface and are removed through very large scale mining operations • During mining, unwanted rock and dirt are removed with the valuable ore – the unwanted material is discarded and potentially harmful to the Earth • If the cost of handling unwanted material out-weighs value of the ore, mineral is no longer classified as an ore • Classification of ore may also change if supple or demand changes – ex. Computer designers develop less costly alternative material

  18. Gems • What makes a ruby more valuable than mica? Rubies are much more rare and more pleasing to the eye than mica • Gems – valuable minerals that are rare and prized for their rarity and beauty (ruby) • Because of their rareness, rubies and emeralds are more valuable than diamonds

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