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Chapter 2 Section 2 Minerals
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What is a mineral? What are the components of a mineral?
Naturally occurring Solid substance Inorganic Orderly crystalline structure Definite chemical composition Ex: Quartz SiO2 (silicon & oxygen) ALL rocks are COMPOSED of minerals
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1. Naturally Occurring Minerals are formed by natural, geologic processes Must naturally occur in nature, cannot be man-made i.e. synthetic gems are not considered minerals. Chillagoe caves,Austrailia
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2 & 3. Inorganic Solid Substance
Minerals are a solid…. not a liquid…not a gas. within temperature ranges that are normal for Earth. Inorganic crystalline solids found in nature Table salt is a mineral inorganic Sugar is not mineral organic Exception: many marine animals secrete inorganic compounds calcium carbonate minerals (coral reefs and in shells)
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4. Crystalline Structure
Atoms are arranged in an orderly, repetitive structure (crystal lattice) Ex: gemstone opal isn’t a mineral has the same elements as quartz (mineral) but NO orderly internal structure
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5. Chemical Composition Au Pyrite “Fools Gold” FeS2
A mineral has a chemical composition defined by a chemical formula Compounds made of 2+ elements Exceptions: gold & silver 1 element (native form)
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How Minerals Form 4 major processes by which minerals form:
Crystallization from magma Precipitation Changes in pressure and temperature Formation from hydrothermal solutions
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Crystallization from Magma
Magma = molten rock Magma cools elements combine to form minerals Ex: quartz & feldspar First to crystallize ones rich in iron, calcium, and magnesium Each mineral begins to crystallize at a different temperature
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Precipitation All water in Earth’s lakes, rivers, oceans etc. contain dissolved substances Water evaporates dissolved substances react to form minerals Change in water temperature dissolved material precipitates out Supersaturated Ex: limestone caves, Great Salt Lake, Utah Mono Lake, CA limestone towers (calcite) formed underwater from calcium rich springs exposed as sea level drops
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Pressure & Temperature
Existing minerals subjected to changes in pressure and temperature Increase pressure Minerals recrystallize while still solid Atoms rearranged forms compacted minerals Change in temperature Minerals may become unstable Form new minerals new temperature
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Hydrothermal Solutions
Very hot mixture of water & dissolved substances Have temps. between 100°C and 300°C Solutions come in contact w/ existing minerals chemical reactions occur new minerals Solutions cool elements combine Supersaturated Ex: Bornite and chalcopyrite (sulfur minerals) formed from thermal solutions
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Mineral Groups Common minerals, together with the thousands of others that form on Earth, can be classified into groups based on their composition. Silicates Carbonates Oxides Sulfates and sulfides Halides Native elements Fluorite - a halide Okenite - a silicate Galena - a sulfide
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Silicate Structure Most common group
Silicon and oxygen combine to form a silicon-oxygen tetrahedron Tetrahedron consists of 1 silicon atom & 4 oxygen atoms silicate Silicon-oxygen tetrahedra can form chains, sheets, & 3-D networks Super strong bonds Ex: olivine-millions of single tetrahedra (Fe,Mg)2SiO4) iron-magnesium silicate
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Silicate Formation Most silicate minerals crystallize from magma as it cools Can occur at or near surface of Earth (temp. and pressure low) Weathering & mountain building form silicates Can occur at great depths (temp. and pressure high) Location during formation & chemical composition of magma determines which silicate minerals will form Olivine: 1200°C Quartz: 700°C
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Carbonates 2nd most common mineral group Contain the elements:
oxygen one or more other metallic elements Calcite (CaCO3): most common carbonate mineral Limestone & marble rocks that are composed of carbonate minerals
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Oxides Contains: Ex: Rutile (TiO2) Ex: Corundum (Al2o3) Oxygen
One or more other elements (usually metals) Ex: Rutile (TiO2) Form as magma cools beneath Earth’s surface Titanium oxide Ex: Corundum (Al2o3) Existing minerals heat & pressure Aluminum oxide
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Sulfates and Sulfides Contain the element sulfur Sulfates = Sulfides =
Ex: Anhydrite (CaSO4) Ex: Gypsum (CaSO4 2H2O) Forms when mineral-rich water evaporates Sulfides = Ex: Galena (PbS) Ex: Pyrite (FeS2) Forms from thermal solutions
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Halides Contains: Halogens from Group 7A in periodic table
Halogen ion One or more other elements Halogens from Group 7A in periodic table Includes fluorine and chlorine Halite (NaCl) i.e. table salt Fluorite (CaF2) used in making steel Forms when salt water evaporates
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Native Elements Minerals in relatively pure form
Ex: Gold (Au), Silver (Ag), Copper (Cu), Sulfur (S), Carbon (C) Native forms of carbon are diamond and graphite Some form from hydrothermal solutions
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