5+minerals

5+minerals - Patterns in Nature Minerals Prepared by Ronald...

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Unformatted text preview: Patterns in Nature: Minerals Prepared by Ronald Parker Earlham College Department of Geosciences Richmond, Indiana Minerals The "building blocks" of rocks, and hence, of Earth. More than 4,000 are known. Dozens of new minerals are discovered annually. Human interest in minerals spans millenia. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Mineral Definition Geologic definition of a mineral is specialized: Naturally occurring. Solid. Formed geologically. Definite chemical composition. Ordered atomic arrangement. Mostly inorganic. Gypsum A mineraloid exhibits some, but not all, properties. Doesn't include "minerals" in the nutritional sense. Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Minerals Developed societies depend on mineral resources. Metals Iron, copper, lead, zinc, nickel, aluminum, etc. Non-metals Gypsum, limestone, aggregate, clay. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Minerals Economically important Drive world economies. Historically important Dictated human history. Iron. Copper. Gold. Diamonds. Gems. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Rocks Rocks are Earth materials made from minerals. Most rocks have more than one kind of mineral. Example: Granite Potassium feldspar. Quartz. Hornblende. Some are monomineralic. Limestone (Calcite). Rock salt (Halite). Glacial ice. Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Crystalline Structure Atoms in a mineral are specifically ordered. A solid with disordered atoms is called a glass. Crystalline structure based on atomic patterns. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Crystals Rare minerals displaying flat external faces. Crystal faces form best in open cavities. Crystals are often prized mineral specimens. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Crystals Constancy of interfacial angles. The same mineral has the same crystal faces. Adjacent faces occur at a diagnostic angle. Faces and angles reflect the atomic arrangement. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Crystal Lattice X-Ray Diffraction (XRD) probes crystal lattices. Unique lattice spacing is used to ID minerals. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Seeing Into Crystals Modern instrumentation allows us to "see" atoms. A beam of electrons passes through material. Atoms scatter electrons, which pass between them. A shadow on the detector indicates a row of atoms. This principle drives the electron microscope. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Atomic Bonding Lattice atoms are held in place by atomic bonds. Bond characteristics govern mineral properties. 5 recognized types of bonds. Covalent. Ionic. Metallic. Van der Waals. Hydrogen. Models depict atoms, bonds, and lattices. Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Polymorphs Same composition but different crystal structure. Polymorphs reveal the importance of bond type. Diamond and graphite are carbon polymorphs (C). Diamond Strong covalent bonds; hardest mineral. Graphite Weak Van der Waals bonds; softest mineral. Diamond Graphite Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Crystal Growth Crystals grow as atoms attach to mineral surfaces. Growth starts from a central seed crystal. Growth expands outward as atoms accumulate. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Crystal Growth Outward crystal growth fills available space. Resulting crystal shape governed by surroundings. Open space Good crystal faces grow. Confined space No crystal faces. Solidification from a melt. Precipitation from solution. Solid-state diffusion. Crystals grow by... Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Mineral Physical Properties Characteristics determined by your 5 senses. Used to ID minerals. Properties depend upon... Chemical composition. Crystal structure. Pyrite Some are diagnostic. Example: Pyrite (FeS2) Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brassy color, sulfur smell when crushed, erroneously mistaken for gold (fool's gold). Minerals have a unique set of physical properties. Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Physical Properties Common properties: Color. Streak. Luster. Hardness. Specific gravity. Crystal habit. Crystal form. Fracture. Cleavage. Needle-like crystal habit Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Physical Properties Less common physical properties: Taste. Smell. Feel. Elasticity. Magnetism. Effervescence. Diaphaneity. Piezoelectricity. Pyroelectricity. Refractive index. Malleability. Ductility. Sectility. Magnetite crystals on a large magnet. Calcite effervesces with acid Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Color Color is diagnostic for some minerals. Olivine is olive green. Azurite is always blue. Quartz (Clear, white, yellow, pink, purple, gray, etc). Some minerals may exhibit a broad color range. Color varieties often reflect trace impurities. Malachite Always green Quartz Many colors Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Streak Color of a mineral crushed on unglazed porcelain. Streak is often a useful diagnostic property. Congruent streak Streak color same as mineral. Magnetite Black mineral; black streak. Incongruent streak Streak color different than mineral. Chromite Black mineral; greenish-brown streak. Hematite Red-brown streak Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Luster The way a mineral scatters light. Two subdivisions. Metallic Looks like a metal. Nonmetallic. Vitreous (glassy). Satiny. Silky. Resinous. Pearly. Earthy (dull). Adamantine (brilliant). Quartz Vitreous luster Satin spar Gypsum Satiny luster Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Hardness Scratching resistance of a mineral. Hardness compared to the Mohs Hardness Scale. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Talc, Graphite Gypsum Fingernail 2.5 Calcite Copper Penny 3.5 Fluorite Apatite Glass - Steel 5.5 Orthoclase Steel File 6.5 Quartz Topaz Corundum Diamond Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Specific Gravity Related to density (mass per volume). Mineral weight over weight of equal water volume. Specific gravity is "heft" How heavy it feels. Pyrite Heavy (SG 5.0) Feldspar Light (SG 2.6) Potassium Feldspar Pyrite "feels" heavier that feldspar. Pyrite Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Crystal Habit Crystal habit is the ideal shape of crystal faces. Ideal growth requires ideal conditions. Many terms are used to describe habit. Cubes Octahedra Blades Hexagonal Prisms Dodecahedra Compound Forms Rhombohedra Tetragonal Prisms Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Crystal Form Minerals vary in crystal face development. Euhedral Good crystal faces; grown in open cavity. Anhedral No crystal faces; grown in tight space. Subhedral Between the two. Face development indicates growth history. Anhedral crystals common; euhedral less so. Amethyst Geode Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Fracture Some minerals lack planes of weakness. Due to equal molecular bonds in all directions. These minerals don't have cleavage; they fracture. Example: Quartz displays conchoidal fracture. Shaped like the inside of a clam shell. Breaks along smooth curved surfaces. Produces extremely sharp edges. Obsidian Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Cleavage Tendency to break along planes of weakness. Cleavage produces flat, shiny surfaces. Described by number of planes and their angles. Sometimes mistaken for crystal habit. Cleavage is through-going; often forms parallel "steps." Crystal habit is only on external surfaces. 1, 2, 3, 4, and 6 cleavages possible. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Cleavage Examples of Cleavage: Muscovite Mica 1 direction 2 directions at 90 Potassium Feldspar 2 directions NOT at 90 Amphibole Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Cleavage Examples of Cleavage: Halite 3 directions at 90 3 directions NOT at 90 Calcite Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Mineral Compositions Only about 50 minerals are abundant. 98.5% of crustal mineral mass is from 8 elements. Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium All others O Si Al Fe Ca Na K Mg 46.6% 27.7% 8.1% 5.0% 3.6% 2.8% 2.6% 2.1% 1.5% 74.3% of crustal minerals !!! Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Mineral Classes Minerals are classified by their dominant anion. Silicates Oxides Sulfides Sulfates Halides Carbonates SSO42- SiO24O2- Rock-forming mins Magnetite, Hematite Pyrite, Galena Gypsum Fluorite, Halite Calcite, Dolomite C Copper, Graphite Native Copper Cl- or FCO32- Native Elements Cu, Au, Malachite (Carbonate) Fluorite (Halide) Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Silicate Minerals Silicates are know as the rock-forming minerals. They dominate the Earth's crust. Oxygen and silicon... Make up 94.7 % of crustal volume, and... 74.3 % of crustal mass. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Silicate Minerals The anionic unit is the silica tetrahedron. 4 oxygen atoms are bonded to 1 silicon atom (SiO44-). Silicon is tiny; oxygen is huge. The silica tetrahedron has a net -4 ionic charge. The silicate unit can be depicted by... Spheres. A ball and stick model. Polyhedra. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Silicate Minerals Silica tetrahedra link together by sharing oxygens. More shared oxygen = lower Si:O ratio; governs... Melting temperature. Mineral structure and cations present. Susceptibility to chemical weathering. Type of Silicate Structure Independent Tetrahedra Double Tetrahedra Ring Silicates Single Chains Double Chains Sheet Silicates Framework Silicates Formula SiO4 Si2O7 Si6O18 SiO3 Si4O11 Si2O5 SiO2 Si:O Ratio 0.25 0.29 0.33 0.33 0.36 0.40 0.50 Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Independent Tetrahedra Tetrahedra share no oxygens - linked by cations. Olivine Group. High temperature Fe-Mg silicate. Small green crystals; no cleavage. Garnet Group. Equant crystals with no cleavage. Dodecahedral (12 sided) crystals. Garnet Kyanite Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Single-Chain Silicates Single-chain structures bonded with Fe and Mg. Pyroxene Group. Black to green color. Two distinctive cleavages at nearly 90. Stubby crystals. Augite is the most common pyroxene. Pyroxene Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Double-Chain Silicates Double chain of silica tetrahedra bonded together. Contain a variety of cations. Amphibole Group - Two perfect cleavages; elongate crystals. Hornblende Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Sheet Silicates 2-dimensional sheets of linked tetrahedra. Characterized by one direction of perfect cleavage. Mica Group Biotite (dark) and Mucsovite (light). Clay Mineral Group Feldspar weathering residue; tiny. Muscovite Mica Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Framework Silicates All 4 oxygens in the silica tetrahedra are shared. Feldspar Group Plagioclase and potassium feldspar. Silica (Quartz) Group Contains only Si and O. Potassium Feldspar Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Gems Minerals with special value. Rarity. Beauty. Color. Interaction with light. Aquamarine Beryl Dispersion. High refractive index. Watermelon Tourmaline Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals Diamonds Diamonds originate under extremely high pressure. ~ 150 km deep in the upper mantle. Pure carbon is compressed into the diamond structure. Rifting causes deep mantle rock to move upward. Diamonds are found in kimberlite pipes. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 5: Patterns in Nature: Minerals ...
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This note was uploaded on 02/22/2012 for the course CE 70 taught by Professor Johnson during the Fall '07 term at Berkeley.

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