Chapter 3.ppt - Chapter 3 Earth Materials Minerals and...

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Unformatted text preview: Chapter 3: Earth Materials: Minerals and Rocks About Earth Materials • All Earth materials are composed of atoms bound together. • Minerals are composed of atoms bonded together and are the building blocks of rocks. • Rocks are composed of minerals and they record various geologic processes. What Are Minerals? Minerals are the building blocks of rocks. Minerals: the building blocks of rocks Definition of a mineral • Naturally occurring • Inorganic - but organic processes may be responsible for many minerals • Solid – ice is mineral, water is not • Possess an orderly internal structure of atoms • Have a definite chemical composition- but sometimes complex and often allows a liberal substitution of some elements in the crystalline structure Mineraloid - lacks an orderly internal structure example-opal Composition and Structure of Minerals • Elements • Basic building blocks of minerals • Over 100 are known • Atoms • Smallest particles of matter • Have all the characteristics of an element Periodic Table of the Elements The Structure of Matter Atomic nucleus: protons and neutrons. Electrons: cloud of moving particles surrounding the nucleus. Example: the carbon atom (C) The Structure of Matter Atoms • Nucleus – central part of an atom that contains • Protons – positive electrical charges • Neutrons – neutral electrical charges • Energy levels, or shells • Surround nucleus • Contain electrons – negative electrical charges Example: The Carbon Atom electron cloud atomic nucleus Carbon has 6 electrons… …and a nucleus of 6 protons … …and 6 neutrons having no charge. electron (–) proton (+) neutron Atoms • Atomic number is the number of protons in an atom's nucleus • Bonding of atoms • Forms a compound with two or more elements • Ions are atoms that gain or lose electrons • Isotopes • Have varying number of neutrons The Structure of Matter Many isotopes are radioactive and emit energy and particles Example: the carbon atom (C) typically has 6 neutrons and 6 protons (called C12), but there are also small amounts of C13 and C14. C14 is radioactive The Structure of Matter Chemical reactions – interactions of the atoms of two or more elements in certain fixed proportions. Example: Na+ + Cl- = NaCl The Structure of Matter Minerals are chemically bonded atoms (chemical compounds) • Ionic bonds – one atom gains an electron, one atom loses an electron • Covalent bonds – atoms share electrons, results in a very strong bond • Metallic Bonds – happens among the transition elements, electrons are freely mobile Electron Transfer: Ionic Bonds Sodium (Na+) + chlorine (Cl-) = NaCl (halite) Electron Transfer: Ionic Bonds Sodium (Na+) + chlorine (Cl-) = NaCl (halite) Each sodium ion (circled in red) is surrounded by 6 chloride ions (circled in yellow), and vice versa. Electron Sharing: Covalent Bonding Electron Sharing: Covalent Bonds Carbon atoms in a diamond Metallic Bonding Native Copper – Metallic Bonds The Structure of Minerals How do minerals form? Crystallization – atoms come together in the proper proportion and proper arrangement The Structure of Minerals Electrical charges of atomic ions Cation – positively charged Anion – negatively charged Atomic ions arrange themselves according to charge and size. The Structure of Minerals The Structure of Minerals When do minerals form? • During cooling of molten rock • During evaporation of water • Upon changes in temperature and pressure on existing minerals Minerals Physical properties of minerals • Crystal form (shape) • Luster • Color • Streak • Hardness • Cleavage • Specific gravity - density Physical Properties of Minerals crystal habit (unrestricted growth) Physical Properties of Minerals Pyrite and its crystal habit Crystal habit – Polymorphs form under different temperatures and pressures Luster – The Way a Mineral Reflects Light Type Metallic Vitreous Resinous Description Example Shiny like a metal Pyrite (polished knife blade) Shiny like glass – can Quartz be dark or light Appearance of resin or Sphalerite amber or dried pine sap Dull Earthy appearance Kaolinite Pearly Milky “rainbow” reflectance like a pearl – inside of seashell Gypsum Greasy Oily appearance Halite Fibrous appearance – has a sheen The brilliant luster of precious gems Asbestos Silky Adamantine Diamond Luster Metallic Vitreous – both specimens below note that specimen can have Some color doesn’t have to be clear Luster Resinous Pearly Dull Luster Greasy Vitreous Compare to Silky Adamantine Color – is diagnostic for the mineral olivine (Fosterite) Color – typically the least useful property Streak Diagnostic of some minerals. Hematite comes in a metallic looking form, but its streak is still red. Hardness – the resistance of a mineral surface to scratching Cleavage versus Fracture • cleavage describes the tendency of minerals to break along planes of weak bonding •Fracture planes of weakness absent Physical Properties of Minerals Mica and its cleavage Conchoidal fracture Specific Gravity (density) This can be diagnostic of the composition of a mineral SG is defined as the ratio of the weight of the mineral to the weight of an equal volume of water. (the mass in grams of one cubic centimeter). Density = mass/volume so they are essentially the same To measure SG, weigh mineral. Weigh the water it displaces SG is ratio: (wt. Rock)/(wt. Water) Other Mineral Properties Other properties • • • • • • • • Taste Smell Elasticity Malleability Feel Magnetism Double Refraction (or Birefringence) Reaction to hydrochloric acid Taste Halite is the mineral equivalent of common table salt - principal component of evaporate deposits Smell Arsenopyrite has the order of garlic when struck Elasticity All minerals exhibit elasticity. When put under stress, they change shape but when the stress is released, they return to their original shape. This is perfect elasticity. A mineral is ductile if it deforms (flows) under high stress. Calcite (a principal component of marble) is ductile in the Earth when put under pressure. It slides along crystalline planes. Asbestos fibers can be woven into a fabric, they can be pulled apart in thins strands, which act like thread. Elasticity determines the velocity of elastic waves in a rock. Olivine is anisotropic-the velocity depend on the direction of wave propagation-flow in upper mantle determines direction of crystals and hence direction of highest velocity. Malleability When placed under stress, they change shape (do not fracture) and do not return to their original shape, usually associated with metallic bonding Metallic gold can be pounded out to a very thin sheet. Feel Soapstone feels like soap, it is soft and easily rubbed off. Birefringence and index of refraction Also called double refraction. The speed of light depends on the polarization of the light relative to the crystal orientation. Light separates into two waves, one traveling faster than the other. The index of refraction (Velocity of light in air divided by velocity in rock) differs for these two waves. Is usually between 1.4 and 2.0 Reaction to acids (chemical tests in general) Dilute HCl used to detect carbonates. Calcite (Calcium carbonate) reacts strongly with hydrochloric acid to create carbon dioxide and calcium chloride. Dolomite (Calcium Magnesium Carbonate CaMg(CO3)2) reacts only slightly when scratched. Reaction with Acid (HCl) Fluorescence White light UV Light Classes of Rock-forming Minerals Chemical classes of minerals: • • • Silicates – contain O and Si Carbonates – contain C and O Oxides – contain O and metallic cations • Sulfides – contain S and metallic cations • Sulfates – contain SO4 and metallic cations Classes of Rock-forming Minerals Chemical classes (cont.): • • • Halides – contain Cl, F, I, or Br Hydroxides – contain OH Native elements – masses of all the same element metallically bonded • Phosphates – contain P and O Mineral Groups • Rock-forming silicates • Most common mineral group – about 95% of all minerals • Contain the silicon-oxygen tetrahedron (molecule) • Four oxygen atoms surrounding a much smaller silicon atom • Combines with other atoms to form the various silicate structures The Silicate Minerals Why silicates are the most abundant mineral group on the Earth’s surface Oxide Minerals (metal+O, H2O, Fe2O3, Al2O3) Includes: Hematite (Fe2O3) Corundum (Al2O3) Magnetite (Fe3O4) Spinel MgAl2O3 Ice H2 O Also the Hydroxides like Goethite HFeO2-component in rust Halide Minerals - are primarily compounds of the Halogen elements F,Cl,Br,I in which a halogen is the principal anion. Includes: Halite (salt) NaCl Fluorite CaF2 Low temperature and evaporate deposits Carbonate minerals (metal+CO32-) A major rock-forming group Found in the rocks limestone and marble Includes: Calcite CaCO3 Siderite FeCO3 Rhodochrosite MnCO3 Dolomite CaMg(CO3)2 Malachite Cu2(CO3)(OH)2 Carbonates Sulfates (metal+SO42-) • Typically found as evaporite deposits – Economically important • Example: Gypsum (CaSO4) Sulfides (metal + S ) 2- • Useful ore materials – Pb, Hg, Fe, Zn, Cu The native elements Phosphate Minerals (Metal + PO42-) • Apatite - CaPO4 Some phosphates are mined for fertilizers Key terms and concepts Anion Atomic mass Atomic number Carbonate Cation Cleavage Color Covalent bond Crystal Crystal habit Key terms and concepts Density Electron sharing Electron transfer Erosion Fracture Grain Hardness Hydrothermal solution Igneous rock Ion Ionic bond Isotope Key terms and concepts Luster Magma Metallic bond Metamorphic rock Mineral Mineralogy Mohs scale of hardness Ore Oxides Polymorph Precipitate Rock Rock cycle Key terms and concepts Sediment Sedimentary rock Silicate Specific gravity Streak Sulfate Sulfide Texture Trace element Vein Weathering ...
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