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Chapter 14 Minerals & Ores
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Mineral A naturally occurring, inorganic, crystalline solid with a definite chemical composition Rock containing one or more minerals (or metals) (or metals) Sources of elements or compounds important to industry or agriculture Ores
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Minerals Almost 4000 minerals found to exist 3 classes of matter: elements, compounds, & mixtures Elements: made of same kind of atom (same number of protons) Native mineral: a mineral which is a pure element Ex: gold, silver, aluminum, etc.
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Compounds: 2 or more elements combined in a fixed ratio Ex: quartz Most minerals are compounds Pure substance: made of only 1 element or 1 compound
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Mixtures: several elements or compounds combined but not in a fixed ratio, proportions can vary because they are not bonded chemically Ex: salt water – amount of salt in water can vary Rocks But minerals are never mixtures!
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Mineralogists Geologists who specialize in identifying minerals Look at a properties, do tests
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Characteristics of Minerals 1) Color Many minerals have same color Some colors due to impurities in mineral Ex: Quartz Color can change when exposed to air
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Characteristics of Minerals 2) Streak Color of a mineral’s powder on unglazed porcelain A mineral’s streak does not change due to impurities Better indicator than color alone
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Characteristics of Minerals 3) Luster: Quality and intensity of light reflected from its surface Types: Metallic Vitreous (glassy) Pearly Adamantine (diamond) Dull Greasy Resinous Earthy
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Characteristics of Minerals 4) Crystal Shape Each mineral has a characteristic crystal shape with fixed angles Crystals enlarge by adding particles (Accretion)
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Characteristics of Minerals 5) Cleavage Characteristic of splitting along certain planes due to weak bonding
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Characteristics of Minerals 6) Fracture: Characteristic way of breaking but not in cleavage planes Types: Conchoidal – smooth curved surfaces (Ex: obsidian, flint) Fibrous – splinters or fibers (Ex: asbestos) Uneven – irregular & rough Hackly – fine, sharp points (Ex: iron, copper)
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Characteristics of Minerals 7) Hardness Ability to withstand scratching & abrasion Hardness test – scratch the mineral with various objects & rate it The Mohs scale: 1-10 Talc = 1, softest Diamond = 10, hardest
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Characteristics of Minerals 8) Specific Gravity Ratio of the mass of a substance with the mass of an equal volume of water at 4°C Can sometimes estimate just by lifting (some rocks feel lighter)
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14B-2 Characteristics of Minerals (cont.) 9) Flame test Wire dipped in mineral powder put in flame Some minerals produce a characteristic color when you burn them
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Characteristics of Minerals 10) Acid test Put hydrochloric acid on the mineral and some minerals give off bubbles (fizzes – called effervescence) Used to identify carbonates, sulfides, & sulfites
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Characteristics of Minerals 11) Magnetism Some minerals can attract bits of iron Ex: magnetite or loadstone used in 1 st compass
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Characteristics of Minerals 12) Radioactivity Can use radiation detector to find radioactive minerals (contain uranium) Ex: pitchblende
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Characteristics of Minerals 13) Luminescence Mineral glows due to absorbing ultraviolet light Fluorescent: glows while under the light Ex: Calcite Phosphorescent: continues to glow when light removed
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Characteristics of Minerals 14) Refraction Bending light passing through mineral Some produce double refraction (double image)
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BW Prepare for quiz on 14B
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