Published on February 16, 2008
Planet Earth:Minerals: Planet Earth:Minerals © M. L. Anderson; 2005 The Rock Cycle: The Rock Cycle The Rock Cycle: The Rock Cycle Stone Age: Stone Age Discoveries of ways to extract and use Earth’s minerals profoundly altered the course of human history. Stone Age consisted of 3 pre-metallurgic periods. Bronze Age: Bronze Age Tin + Copper + charcoal (heat) = Bronze 3300BCE 1200BCE In Homer’s Illiad, the weapons are mostly bronze. Iron was very rare and used as currency in the form of ingots or pellets. Iron Age: Iron Age The discovery of carburization, the process of adding carbon to iron, led the way to the Iron age @ 1200BCE. The molten metal was then repeatedly hammered and folded to create wroght iron. Industrial Age: Industrial Age Fueled by the discovery of how to exploit coal reserves and how to harness steam power. Automobile Age: Automobile Age Occurred because humans found vast oil reserves in shallow rocks within the Earth’s crust. Computer Age: Computer Age Relies on the discovery of how to control the movement of electrons through wafer-thin slices of silicon. Rocks: Rocks Most rocks contain 2 to 5 abundant minerals plus trace amounts of several other minerals. Granite: K feldspar Quartz Na Feldspar, Biotite mica, Hornblende, Muscovite mica, Pyroxene. Matter: Matter Matter: Anything that has mass and occupies space is matter. Matter occurs in 3 phases: solid, liquid, gas. Minerals are solids. Minerals: Minerals Mineral: a naturally occurring, inorganic crystalline solid with a definite chemical composition and characteristic physical properties. Water is not a mineral. Ice is. A: Iron Pyrite / B: Amethyst Elements: Elements All matter is made up of chemical elements. Elements are composed of atoms. Atoms are the smallest units of matter that retain the characteristics of an element. There are 88 naturally occurring elements, @ 12+ artificially produced elements. Mineral Diversity : Mineral Diversity More than 3,500 minerals have been identified, but only @ 2 dozen are common. Only 8 elements make up the bulk of the earth’s crust. Oxygen and Silicon constitute 74% of the earth’s crust and nearly 84% of the atoms available to form compounds. O 46% Si 27% Al 8.1% Fe (iron) 5% Ca 3.6% Na 2.8% K (potassium) 2.6% Mg 2.1% others 1.5% Atoms: Atoms Atoms consist of: A nucleus with 1 or more protons : with a + charge. Also in the nucleus are Neutrons which are electrically neutral. Electrons encircling the nucleus, which are - charged. Electrons orbit the nucleus in one or more electron shells. The element is determined by the # of protons in the nucleus. Atomic number is determined by the # of protons. Slide16: Ie Hydrogen Helium Carbon Uranium # if p in nucleus: 1 2 6 92 atomic # 1 2 6 92 atomic mass # 12,13,or 14 Atoms are characterized by their atomic mass #: Adding the # of protons & neutrons together. Atoms of the same element may have different atomic mass #’s. The same element with different mass #’s are : isotopes. Isotopes are unstable and spontaneously change to a stable form. This process is radioactive decay. All isotopes behave the same chemically. Bonding: Bonding Bonding: the process whereby atoms are joined to other atoms. When 2 or more different elements are bonded, the substance is a compound. Most minerals are compounds with a few exceptions: Gold, silver, graphite, diamond. Atoms: Atoms With the exception of Hydrogen (one p+ and 1 e-) The innermost shell of an atom contains no more than 2 e-‘s. The outermost shell will vary but will never have more than 8 e‘s. The e’s in the outermost shell are responsible for bonding. The two main types of Chemical Bonds: Ionic and Covalent. Two others: Metallic and Van der Waals. Ionic Bonding : Ionic Bonding Nobel gasses have complete outer shells. These do not react readily with other elements to form compounds. Interactions between atoms tend to produce compounds with electron configurations similar to noble gasses. They try to fill their outer shell. Ionic bonding: the transfer of one or more e- from one atom to another. Ionic Bonding: Ionic Bonding Ionic bonding: the transfer of one or more e- from one atom to another. The electron is lost by the Na and is transferred to the Cl. Addition of 1 e- to Cl gives the configuration of a noble gas. I.e.: NaCl = halite or table salt: sodium chloride. Ionic Bonding: Ionic Bonding Na Cl 11 protons 17 protons 11 electrons 17 electrons 2 / 8 / 1 2 / 8 / 7 1e- - to fill outer shell making 8e- Covalent Bonding : Covalent Bonding Covalent bonds form between atoms when their shells overlap and electrons are shared. The sharing of electrons. Carbon had 4 e- in it’s outer shell. If these are shared with another carbon atom, each has the configuration of a noble gas. Among the most common minerals, the silicates: Si forms partly covalent bonds with Oxygen. Covalent Carbon Bonds: Covalent Carbon Bonds Covalent bonds formed by adjacent atoms sharing electrons in a diamond. Three-dimensional framework of carbon atoms in a diamond. Covalent bonds in graphite. The sheets are held together by Van der Waals bonds. Weak bonds between sheets. Van der Waals Bonds: Van der Waals Bonds Some electrically neutral atoms have no electrons available for bonding, they nevertheless have a weak attractive force when they are in close proximity. This weak force is a Van der Waals or Residual bond. The carbon atoms in graphite are covalently bonded together to form sheets, but the sheets are weakly held together by Van der Waals bonds. Metallic Bonding: Metallic Bonding Metallic Bonding: is an extreme type of electron sharing. The electrons in the outermost shell of metals (gold, silver, copper) are readily lost and move about from one to another. This e- mobility accounts for their metallic luster (reflecting light) and provides good electrical and thermal conductivity, And can be easily reshaped. Slide26: Metallic Bonding Minerals: Minerals Minerals : Most minerals are compounds of two or more elements. Quartz: 1 Si + 2 O = SiO2 Orthoclase Feldspar: 1 potassium K Al Si3 O8 Some minerals are composed of a single element: Native elements: Gold – Au, Silver – Ag Platinum - Pt, Graphite & Diamond - C Mineral: Mineral Mineral: a naturally occurring, inorganic, crystalline solid, with a narrowly defined chemical composition and characteristic physical properties. Naturally occurring ; excludes all substances manufactured by humans. Synthetics. Inorganic – animal matter and vegetable matter are not minerals, however corals and clams construct their shells of Calcium carbonate, CaCO3 , which is calcite or aragonite. Both are minerals. Mineral: Mineral Crystalline Solid – a solid in which the constituent atoms are arranged in a regular, 3-D framework. Under ideal conditions, such as in a cavity, mineral crystals can grow and form perfect crystals that possess planar surfaces (crystal faces), sharp corners, and straight edges. Natural glass (obsidian) and manufactured glass lack the ordered arrangement of atoms. They are amorphous – w/o form. Mineral: Crystalline Solid: Mineral: Crystalline Solid Consistency of interface angles - regardless of their size, shape or geographic occurrence, the angles of all crystals of the same element are equal, .i.e.: all quartz crystals have the same angles. Many minerals possess cleavage – they break or split along closely spaced, smooth planes. The mineral’s internal structure controls such breakage. (Mica) Chemical Composition: Chemical Composition Some minerals have a range of chemical compositions. : one mineral may substitute for another. I.e.: olivine (MgFe) 2SiO4 , means that either Mg or Fe (iron) or both may combine with the SiO4. One element may substitute for another if the atoms are nearly the same size and the same charge. For most minerals the chemical composition is constant. Quartz: SiO2; Halite: NaCl Physical Properties – are properties such as hardness, color and crystal form. PHYSICAL PROPERTIES OF MINERALS: PHYSICAL PROPERTIES OF MINERALS All minerals possess characteristic physical properties that are determined by their internal structure and chemical composition. Color: Color Metals: color is consistent Ferromagnesian silicate minerals are dark; typically black, brown or dark green or olive (olivine) Others: color varies due to impurities Non-ferromagnesian silicates are rarely dark. Above: pink granite. Below: Diorite. Luster: Luster Appearance of a mineral in reflected light Metallic: shiny or reflective Non-metallic: glassy, vitreous, greasy, waxy, brilliant, dull, earthy. Crystal Form: Crystal Form Crystal Form Common crystals include: 12 sided garnet, 12 sided pyrite Minerals that grow in cavities or are ppt. from hot water (hydrothermal solutions) in cracks and crevices of rocks occur as crystals. Cleavage: Cleavage Cleavage: an important diagnostic property of individual mineral crystals. Not all minerals possess cleavage. Where a mineral will break or split along a smooth plane or planes of weakness determined by the strength of the bonds. Can be characterized by quality: perfect, good poor Cleavage: Cleavage Biotite mica: perfect in one direction; it is a sheet silicate. The sheets of silica tetrahedra are weakly bonded to one another by Fe and Mg ions. Feldspars: have two directions of cleavage that intersect at right angles to each other. Cleavage: Cleavage Halite: has three directions of cleavage – all at right angles. Calcite: also has 3 directions of cleavage – none at right angles.(rhombohedrons) Cleavage: Cleavage Fluorite & diamonds: 4 directions of cleavage. Cleavage can separate two minerals that otherwise look alike. Cleavage: Cleavage Pyroxene mineral augite ; dark green black, cleavage intersect at 90’ ; same hardness as hornblende Amphibole mineral hornblende :dark green black; cleavage intersect at 56’ and 124’. Spherolite: Cleavage in 6 directions. Fracture: Fracture Fracture: mineral breakage along irregular surfaces Chert Orthoclase feldspar Rose quartz Hardness: Hardness Hardness: the resistance of minerals to abrasion MOHS Scale of hardness: 1. talc is the softest 10. diamond Hardness is controlled by internal structure. Specific Gravity: Specific Gravity Specific Gravity: ratio of mineral’s weight to the weight of an equal volume of water. Water = 1. A dimensionless number. FeMg silicates @ 2.7 – 4.3 ; non-FeMg silicates @ 2.6 – 2.9 Metallic minerals galena 7.58 & hematite 5.76; are heavier than non-metallic minerals. Other Properties: Other Properties Double refraction: calcite creates a double image Flexibility: Plastic Effervescence: Calcite will bubble when a drop of HCl is applied. CO2 is released. Dolomite will not react unless powdered. Rock Forming Minerals : Rock Forming Minerals Rocks: solid aggregates of grains of one or more minerals. Most rocks are composed of silicate minerals. Quartz: (SiO2) The most common Igneous Rock: Quartz: (SiO2) The most common Igneous Rock Citrine Amethyst The coloration is from impurities. Quartz: at the bottom of Bowen’s Reactionary series. Last to crystallize, first to re-melt. Most resistant to weathering.: Quartz: at the bottom of Bowen’s Reactionary series. Last to crystallize, first to re-melt. Most resistant to weathering. Smoky Quartz Rose Quartz Mineral Groups: Silicates: Mineral Groups: Silicates Silicate Minerals A combination of oxygen and silica is a silicate. Quartz is pure SiO2 Most silicates have one or more additional elements. Orthoclase feldspar KalSi3O8 Olivine (Mg, Fe) 2 SiO4 Silicates: Silicates Silicate minerals include about 1/3 all minerals and @ 95% of the earth’s crust. Basic building block of all silicate minerals is the silica tetrahedron. = 1 Si and 4 O atoms A 4-faced pyramidal structure. Silicates: Silicates The silica atom has a positive charge of 4 The 4 oxygen atoms have a negative charge of 2 each. 4 (SiO4) -4 a total negative charge of 4-. Because it has a negative charge it combines readily with positively charged ions or shares its O atoms with other silica tetrahedra. Silicates: Silicates Silica tetrahedra may also be arranged so that they join together to form chains of indefinite length. Single chains (pyroxene) form when each tetrahedron shares two of its oxygen atoms with adjacent tetrahedra. This is a silica / Oxygen ratio of 1:3. MgSiO3 Amphibole Minerals : Amphibole Minerals The amphibole minerals have a double-chain structure, in which alternate tetrahedra are cross-linked. The double chain results in a Silicon: Oxygen ration of 4:11. Each double chain possesses a –6 electrical charge. Mg+2, Fe+2, and Al+2 are usually involved in linking double chains. Amphibole Minerals: Amphibole Minerals In sheet structure silicates, three oxygens of each tetrahedra are shared by adjacent tetrahedra. This results in continuous sheets of silica tetrahedra w/ silica to oxygen ratios of 2:5. Continuous sheets also posses a negative electrical charge that is satisfied by positive ions between the sheets. This structure accounts for micas (biotite & muscovite) and the clay minerals. Ferromagnesian Silicates : Ferromagnesian Silicates Contain iron (Fe), Magnesium or both. These are characteristically dark colored and more dense. Includes: Olivine’s, pyroxenes, amphiboles and biotite. Non-ferromagnesian Silicates : Non-ferromagnesian Silicates Lack iron and magnesium Light in color and are less dense than Fe-mg silicates. Most common minerals in earth’s crust: feldspars Potassium feldspars: microcline and orthoclase (KalSi3O2) Plagioclase feldspars: from calcium rich (CaAl2Si2O8) to Sodium rich (NaAlSi3O8) Quartz and muscovite mica are other common non-FeMg silicates. Slide56: One of the most common minerals in earth’s crust: feldspars Carbonate Minerals : Carbonate Minerals Carbonates form sedimentary rocks cover large regions of every continent. Shells, corals, skeletons accumulate to form limestone. Contain negatively charged carbonate ion (CO3)-2. Calcite or calcium carbonate: (CaCO3)2 Carbonate Minerals: Carbonate Minerals Calcite (CaCO3) is the main constituent of sedimentary rock: limestone. Dolomite [CaMg(CO3)2] is formed by the alteration of calcite, replacing it in ancient rocks with Mg. Oxides : Oxides Oxides: an element combined with Oxygen. Iron is commonly bonded to Oxygen. Iron oxides: Hematite – (Fe2)3) and Magnetite (Fe3O4) Important sources of iron ore for steel manufacture Sulfides: Sulfides Sulfides: have a + ion combined with sulfur (S-2) Galena (PbS) Iron Pyrite (FeS) Copper, Led, Zinc Cadmium and Mercury are commonly bonded to sulfur to form sulfide ores. Sulfates: Sulfates Sulfate: an element combined with the sulfate ion (SO4)-2 Gypsum (CaSO4 ) 2H2O Gypsum is mined for plaster and sheetrock. Halides: Halides Halides: contain halogen elements: Chlorine (Cl-1) & fluorine (F-1) Halite: (NaCl) and fluorite (CaF2) Halite is mined for table salt. Native Metals: Native Metals Composed of a single element. Gold, silver, platinum Environmentally Hazardous Rocks: Environmentally Hazardous Rocks Silicates such as feldspar and quartz are harmless in their native states. When crushed or ground-up to a fine powder for processing they become toxic if inhaled. Common exposure to silica dust in mines, stone cutting, building, road construction industries. Silicosis: scarring of lung tissue Coal dust inhaled by coal miners caused “black lung”. Environmentally Hazardous Rocks: Environmentally Hazardous Rocks Asbestos, the industrial name for minerals that crystallize as long, thin fibers. Chrysotile crystallizes as tangled curly fibers. 4 similar varieties of Amphibole crystallize as straight, sharply pointed needles. Asbestos can be woven, is flameproof, chemically inert, extremely strong. Used for brake linings, fire-proof clothing, insulation, shingles, tile and pipe. Inhailed, the fibers can cause Asbestosis and Lung cancer. Serpentine QuarryAlbene Stone Division of the Georgia Marble Co.: Serpentine Quarry Albene Stone Division of the Georgia Marble Co. Serpentine: Serpentine Serpentinites are rocks that formed by hydro-thermal metamorphism of ultra-basic igneous rocks. Serpentines vary greatly in consistency and use: from asbestos to serpentine marble. Serpentine: Serpentine Serpentine is a major rock forming mineral and is found as a constituent in many metamorphic and weather igneous rocks. It often colors many of these rocks green. Most rocks that have a green color probably have serpentine in some amount. Slide69: Serpentine Uses: many industrial applications, including brake linings and fireproof fabrics and as an ornamental stone. Serpentines: Serpentines The following is a list of these minerals, their formulas and symmetry class: Antigorite; (Mg,Fe)3Si2O5(OH)4; monoclinic. Clinochrysotile; Mg3Si2O5(OH)4; monoclinic. Lizardite; Mg3Si2O5(OH)4; trigonal and hexagonal. Orthochrysotile; Mg3Si2O5(OH)4; orthorhombic. Parachrysotile; (Mg,Fe)3Si2O5(OH)4; orthorhombic. Their differences are minor and almost indistinguishable in hand samples. The chrysotile minerals are more likely to form serpentine asbestos, while antigorite and lizardite form cryptocrystalline masses sometimes with a lamellar or micaceous character. Asbestos was used for years as a fire retarding cloth in ceiling tiles, pipe insulation and in brake linings. Its links to cancer have led to the development of alternative materials for these purposes. Acid Mine Pollution: Acid Mine Pollution Copper, Led, Zinc Cadmium and Mercury are commonly bonded to sulfur to form sulfide ores. Mining releases sulfur into local streams, ground water and the atmosphere causing serious air and water pollution. Rain on piles of waste material combines with the sulfur to form hydrogen sulfide and sulfuric acid, poisoning anything down stream or down wind.