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Minerals & Their Formation

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1 Minerals & Their Formation
Chapter 30 Minerals & Their Formation Presented by April Senger

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Minerals A naturally occurring solid substance made up of a single element or compound Minerals are a natural, inorganic solid with a definite chemical composition and a characteristic internal structure Presented by April Senger

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Mineral Facts Quartz is a common mineral with the formula SiO2 where granite is not a mineral because it has many different combinations of minerals (no set formula) The Earth’s crust has 3500 minerals but only 20 of them are in rocks Approximately 20 minerals make up 95% of the Earth’s entire crust Nine of those minerals make up the most common rocks (feldspar, pyroxene, mica, olivine, dolomite, quartz, amphibole, clay and calcite) Presented by April Senger

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Crystal Form The orderly arrangement of atoms in a crystal is expressed in it shape or crystal form Crystals rarely are well formed in nature because they are forced to form in cramped spaces Pyrite has intergrown cubes, quartz has 6-sided prisms that narrow at one end to a point, asbestos forms narrow threadlike fibers, hematite has grape like clusters, etc Polymorphs are made of the same elements but have different shapes such as the carbon arrangement in diamonds & graphite Presented by April Senger

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Concept Check Many minerals can be identified by their physical properties-crystal form, hardness, cleavage, luster, color, streak, and specific gravity. Why is identifying a mineral by its crystal form usually difficult? Well shaped crystals are rare in nature due to the space they have to form in Presented by April Senger

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Hardness Hardness is the resistance of a mineral to scratching Mohs Scale of Hardness on page 539 will be useful in mineral identification You will notice that the items used to test hardness are common even in camping gear Hardness will depend on the atoms arrangements, how close they are together, and the kinds of bonds Presented by April Senger

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Cleavage Cleavage & Fracture are the ways minerals break The breaks occur on planes of weakness for most minerals Muscovite breaks in 1-D planes, Galena breaks in 3-D cubes and Garnet breaks in no set patterns due to strength between its bonds Some minerals fracture or are conchoidal Quartz and olivine have smooth fractures where hematite and serpentine have splinter/fiber like fractures Most fracture irregularly Presented by April Senger

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Concept Check When pieces of calcite and fluorite are scraped together, which scratches which? Note table 30.1 Fluorite is harder than calcite so fluorite will scratch calcite Presented by April Senger

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Luster Luster is the way the surface looks when it reflects light Luster doesn’t depend on color Color is the least accurate way for identification Note: Diamonds are adamantine (bright/brilliant) but have different colors Examples might be metallic, vitreous, resinous, greasy, pearly, silky or adamantine Presented by April Senger

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Streak The color of a mineral in its powdered form is called its streak We usually rub a mineral across a porcelain plate and it leaves a thin layer of powder Hematite and magnetite comes in a variety of colors but always has the same streaks Nonmetallic luster usually give us a white streak White is not as useful in ID because it could be white, clear or no streak on a white plate What would it mean if it was no streak? Presented by April Senger

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Specific Gravity SG is the ratio between the weight of a substance and the weight of an equal volume of water Gold has a SG of 19.3 meaning 1 cubic cm of gold is 19.3 x weight of 1 cubic cm of water Presented by April Senger

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Concept Check Why are their no units for SG? Density of Mineral = cancel of units Density of Water Presented by April Senger

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Taste Test & Acid Test Halite or NaCl has a distinct taste Some minerals are poisonous so it is not recommended to go around licking minerals Carbonate minerals fizz when a drop of hydrochloric acid HCl is put on it Bubble of carbon dioxide are produced Only some minerals react with HCl, some need a little scratch first and others don’t react at all Acid tests commonly leave marks on the mineral Presented by April Senger

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Rock Forming Minerals Some minerals are made of only one element but they often combine to create the rocks we find on Earth There are 115ish elements recognized, 88 make ups the Earth’s crust The 88 elements combine to form 3400 different types of minerals Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, & Magnesium make up 98% of the Earth’s crust Over half of that mass is Oxygen Presented by April Senger

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Silicates Oxygen is the most common element followed by Silicon Silicon is never found by itself and forms very strong bonds Silicon and Oxygen form a group called the Silicates and is the largest group of minerals Feldspar (most abundant mineral on Earth) is made of Si, O, Al, Na, K, & Ca Quartz (2nd most abundant) is Si2O Silicates always come in tetrahedral shape Presented by April Senger

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The Oxides Oxides contain oxygen with one or more metals Some metals might be Fe (hematite and magnetite), Cr (chromite), Mn (pyrolusite), Sn (cassiterite), & U (uraninite) Oxides are used in industrial and technological manufacturing Presented by April Senger

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Carbonate Carbonate have a simple triangular structure It has one central carbon and three oxygens Calcite CaCO3 and Dolomite CaMg(CO3)2 and the main minerals found in the group of rocks called limestone Presented by April Senger

18 The Sulfides & Sulfates
The main element is Sulfur Sulfides bond with metal ions and look metallic such as pyrite Sulfates have sulfur with 4 oxygens in a tetrahedral shape Gypsum (calcium sulfate) is one of the most abundant sulfates and is used in plaster of paris Presented by April Senger

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Minerals to Rocks? Crystallization is the process where minerals form rocks You can form crystals from cooled magma or water solutions Minerals/Rocks must be degrees C to melt Minerals might melt all the way or partially creating different kinds of rocks Presented by April Senger

20 The Three Kinds of Magma
Basaltic magma is low in silicon content Basalt crystals are dark in color and can be found in places like the Hawaiian Islands Andesitic magma is medium in silicon content and is produced by partial melting of basaltic ocean crust Andesite (in the Andes of S America) can undergo partial melting for form granitic magma Granitic magma is high in Si content and generally forms granite or granitic rocks when cooled Presented by April Senger

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Cooling Down Minerals that have the highest melting points (lowest levels of Si) crystallize first If they cool quickly, the crystallization happens fast and there isn’t much time for large crystals to form If they cool slowly, it give the crystals longer time to form and precipitate out of the magma thus forming bigger crystal Presented by April Senger

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Concept Check Granite has well formed and large crystals. Where might you find granite beds? On the surface of the crust or buried deep inside the Earth? Deep so that the Earth acts like a blanket and cools it slower Presented by April Senger

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Chemical Sediments Minerals that precipitate from water when dissolved and form either carbonates or evaporites The carbonates are mainly calcite or dolimite formed from shells that disolve and are compressed into limestone on the ocean floors Stalagtites and Stalagmites and inorganic ways for carbonate to form Gypsum, anhydrite, and halite are minerals that precipitate out when water bodies leave them behind Presented by April Senger

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Concept Check What is a rock? A rock is more than one mineral They may also have some of the four characteristics of a mineral but not all Minerals are a natural, inorganic solid with a definite chemical composition and a characteristic internal structure Presented by April Senger

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