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Identifying Minerals

Identifying Minerals. Rock-Forming Minerals Over 2000 known minerals, many are rare Common minerals are rock-forming minerals Most R-F minerals are silicate The minerals are identified by their physical properties The study of minerals is mineralogy. Identification by Inspection.

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Identifying Minerals

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  1. Identifying Minerals • Rock-Forming Minerals • Over 2000 known minerals, many are rare • Common minerals are rock-forming minerals • Most R-F minerals are silicate • The minerals are identified by their physical properties • The study of minerals is mineralogy

  2. Identification by Inspection • Colour is the first and most easily observed mineral property • Colour is the least useful property, because many different minerals have similar colours • Traces of impurities can turn colourless minerals into coloured minerals • Luster is the way the mineral shines in reflected light • Lusters are either metallic or nonmetallic • Nonmetallic luster can be vitreous (like glass), pearly, resinous, or glassy. • Diamond has adamantine luster. • Other terms are greasy,oily, dull, and earthy

  3. Identification by Tests • The streak of a mineral is the colour of its powder, obtained by rubbing it on an unglazed white tile called a streak plate. • The cleavage of a mineral is its tendency to split easily or separate along flat surfaces • Some minerals tend to break along non-cleavage surfaces, called fracture • The hardness of a mineral is its resistance to being scratched, diamond is the hardest, talc is the softest • Friedrich Mohs devised the hardness scale from one to ten http://academic.brooklyn.cuny.edu/geology/grocha/mineral/cleavage.html

  4. Specific Gravity • Specific gravity is the ratio of the weight of a mineral to the weight of an equal volume of water • S-G tells you how many times as dense as water the mineral is • Nearly all minerals are denser than water • Their specific gravities are greater than 1 • The weight of the mineral is found by weighing it in air • Then the mineral is weighed underwater • The second weighing indirectly gives the weight of an equal volume of water • The sample weighs less underwater due to buoyancy • Archimedes’ principle states that this loss in weight is equal to the weight of the displaced water • Specific gravity = weight of sample in air weight of equal volume of water • = weight of sample in air loss of weight in water

  5. Acid Test • Calcite is the principle mineral in limestone and marble • Calcite is calcium carbonate, and a drop of weak hydrochloric acid will cause it to fizz. • The bubbles are carbon dioxide gas

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