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Unit 3.1: Minerals

OLD GEOLOGISTS NEVER DIE…. Unit 3.1: Minerals. I. Characteristics of Minerals. CaTiO 3. CsCl. Minerals have five characteristics: Inorganic : from physical processes, not living organisms There are a few exceptions Natural : not man-made

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Unit 3.1: Minerals

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  1. OLD GEOLOGISTS NEVER DIE… Unit 3.1: Minerals

  2. I. Characteristics of Minerals CaTiO3 CsCl • Minerals have five characteristics: • Inorganic: from physical processes, not living organisms • There are a few exceptions • Natural: not man-made • Ex: cubic zirconium is not a true mineral b/c man-made • Solid: not a liquid or a gas • Crystalline structure: the arrangement of atoms relative to all other atoms in a mineral • Chemicalcomposition: based on ratio of elements within the mineral

  3. Purpose of mineralogy: knowing the structure and composition of a mineral can tell you: • Physical properties of the mineral • **Where and how the mineral was formed** • How it can be used

  4. II. Crystal Formation • Two processes by which minerals crystallize: • Precipitation: when water evaporates, the minerals and salts that were dissolved in the water are left behind, form crystals. • If water evaporates quickly, then the crystals that form are smaller, contain more impurities (fast = smaller) • If water evaporates slowly, then allows larger, more pure crystals to form (slow = larger)

  5. Change in temperature: as temperatures decrease, causes liquids to condense into solids that can form a structured arrangement of minerals • Ex: ice forms a crystalline structure when liquid water cools. • Ex: magma (molten rock) cools to become igneous rock. • Slow drop in temperature allows larger crystals to form • Quick drop in temperature leads to smaller crystals

  6. Differences in Mineral Formation: • Difference in composition: if you change some of the ions while the mineral is forming, it can change some properties of the mineral • Ions of similar size are interchangeable, yield range of colors • Sometimes “impurities” can cause variations in minerals

  7. Differences in structure: if you change the arrangement of the elements, you’ve changed the mineral. • Called polymorphs: same element but different arrangement of atoms • “poly” = many; “morphs” = forms • Also called “allotropes” • For example: carbon has 3 polymorphs • Diamond: hard b/c all covalent bonds • Graphite: soft b/c layered sheets, weak electrical bonds • Buckminsterfullerene (C60): also called “buckyballs”

  8. Mineral Classes All minerals made up of only 8 elements: O, Si, Al, Fe, Ca, Na, K, Mg Silicates: SiO44- Non-Silicates Light-colored Dark-colored Oxides O2- Carbonates CO32- No Fe or Mg Because Fe and/or Mg SO42- Sulfates Less dense; makes up continental crust More dense; makes up oceanic crust Sulfides S2- Halides Br-, Cl-. F- Au, Ag, Sn, Pb, Fe Native Elements

  9. III. Mineral Classes • Over 4000 known minerals but all are made up of only 8 elements: • O • Si • Al • Fe • Ca • Na • K • Mg

  10. Can be divided into two broad categories: • Silicates: SiO44-; most common • Negatively charged, so attracted to… cations! • Silicate ion forms a tetrahedral structure; different minerals arrange the silicate tetrahedron in different ways • Nonsilicates: not silicon-based

  11. Amphibole Olivine Pyroxene Biotite C. Silicates can be subdivided into twoclasses: • Dark-colored: contain Iron (Fe) and/or Magnesium (Mg) • Fe and Mg are denser (and darker) elements so these silicates are “heavier”; commonly found in oceanic crust • Examples: • Olivine: simple tetrahedral arrangement • Pyroxene: tetrahedra form single chains • Amphibole: tetrahedra form double chains • Biotite: tetrahedra form “sheets”

  12. Clay Feldspar Quartz Muscovite • Light-colored: do not contain Iron or Magnesium • These silicates are not as dense, so not as heavy • Commonly found in continental crust • Examples: • Feldspar (most common) • Quartz • Muscovite • Clay

  13. D. Nonsilicates do not build on silicon, are less common, but are important economically. • Six classes of nonsilicates: • Oxides: O2-; ex: for mining ores of iron • Carbonates: CO32-; used in cement • Sulfates: SO42-; used in plaster • Sulfides: S2-; for mining ores of lead, zinc, copper, mercury • Halides: Cl1-, F1-, Br1-; for making salt, fertilizer • Native elements: Au, Ag, Sn, Pt; used for jewelry, electrical conductors, trade/currency, medicines

  14. IV. Eight Properties of Minerals • Luster: how it reflects light • Depends on smoothness of surface at the atomic level • Characterized as: • Metallic (shiny) • Nonmetallic • Glassy • Earthy • Pearly • Silky • Waxy

  15. Color: results from absorption and reflection of wavelengths of light • Arrangement of atoms determines how light passes through and interacts with the atoms in the mineral. • Color can be misleading due to impurities: • “Quartz” has many different colors depending on which cations bind to the tetrahedron.

  16. Streak: color of the residue when scratched onto tile plate • Much more reliable indicator than color: two minerals that look “black” will “streak” their true color • Two quartz minerals may be different colors, but will have same streak • Hardness: resistance to scratching • Depends on the type of bonding that holds the minerals together: • Minerals held together by covalent bonds are harder than those held together by ionic bonds b/c covalent bonds holds atoms closer together • Mohs hardness scale rates this: • Diamond is hardest mineral = 10 • Graphite is softest mineral = 1

  17. Density: the mass of a mineral contained within a certain volume • Depends on how tightly the atoms are packed: • If packed tightly, then more dense • If packed loosely, then less dense

  18. Gold: SG of 20 Fool’s Gold: SG of 5 • Specific Gravity: compares the mass of a mineral to an equal mass of water • Depends on atomic weights and how tightly atoms are packed: • Tighter packing = higher specific gravity • Examples: • Specific gravity of 24K gold is 20 • Specific gravity of most rock-forming minerals is 2.5

  19. Crystal Faces: flat, smooth exterior surfaces that are characteristic of each mineral. • Depends on the arrangement of the atoms that make up the mineral • Salt: cuboidal • Garnets: dodecahedrons (12-sided) • Magnetite: octahedron (8-sided) • Even if the shape is not geometric, each mineral still has a characteristic shape that helps to identify it.

  20. Cleavage: the planes along which a crystal breaks and the shape of the resulting fragments • Crystal breaks where bonds are weakest, depends on how/where atoms are bonded. • Silicon tetrahedra arrangement allows us to predict type of cleavage: • Simple = no cleavage • Single chain = 90° cleavage • Double chain = 60° and 120° • Sheets = …sheets

  21. Fracture: when a mineral breaks irregularly, not along a plane • Does not result in a regular, predictable, characteristic shape, so not a “true” property of minerals • Can be irregular or conchoidal: • Conchoidal: bowl-shaped fracture

  22. Warm-up answers for this unit:

  23. Warm-up answers for this unit:

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