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Understanding Minerals: Composition, Formation, and Classification

This section delves into the definition and characteristics of minerals, outlining their naturally occurring, solid, inorganic nature, and orderly structure with a defined chemical composition. It examines how minerals form through processes like crystallization from magma, precipitation, changes in temperature and pressure, and hydrothermal solutions. The classification of minerals into groups such as silicates, carbonates, oxides, sulfates, and halides is discussed, emphasizing their chemical compositions and common examples. Understanding these fundamentals sheds light on the essential role minerals play in the Earth’s geology.

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Understanding Minerals: Composition, Formation, and Classification

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  1. Chapter 2 Section 2 Minerals

  2. 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) • ALLrocks are COMPOSED of minerals

  3. 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.

  4. 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)

  5. 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

  6. 5. Chemical Composition Pyrite “Fools Gold” FeS2 Au • A mineral has a chemical composition defined by a chemical formula • Compounds made of 2+ elements • Exceptions: gold & silver  1 element (native form)

  7. How Minerals Form • 4 major processes by which minerals form: • Crystallization from magma • Precipitation • Changes in pressure and temperature • Formation from hydrothermal solutions

  8. 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

  9. Precipitation Mono Lake, CA limestone towers (calcite) formed underwater from calcium rich springs  exposed as sea level drops • 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

  10. 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  stable @ new temperature

  11. 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

  12. Mineral Groups Fluorite - a halide Okenite - a silicate Galena - a sulfide • 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

  13. Silicate Structure (Fe,Mg)2SiO4) iron-magnesium silicate • 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

  14. 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

  15. Carbonates • 2nd most common mineral group • Contain the elements: • carbon • oxygen • one or more other metallic elements • Calcite (CaCO3): most common carbonate mineral • Limestone & marble  rocks that are composed of carbonate minerals

  16. Oxides • Contains: • 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

  17. Sulfates and Sulfides • Contain the element sulfur • Sulfates = • Ex: Anhydrite (CaSO4) • Ex: Gypsum (CaSO4  2H2O) • Forms when mineral-rich water evaporates • Sulfides = • Ex: Galena (PbS) • Ex: Pyrite (FeS2) • Forms from thermal solutions

  18. Halides • Contains: • 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

  19. 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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