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Elements to Minerals Reading this week: Ch. 2 and App. C Minerals Environmental Significance I. II. Environmental Significance Elements: Definitions, elemental composition of the Earth III. Mineral Definition IV. Mineral Identification V. Major groups of minerals Economic resources Foundations for roads and buildings affected by mineral properties Elements Definitions Construction materials for buildings and monuments Health hazards such as radon Structure of the Earth Elements: # of protons = # of electrons Isotopes: Same # of protons, Different # of neutrons Early differentiation into core, mantle, and crust 1 Elemental Composition of the Earth Whole Earth Elements to Minerals Definitions (continued) Crust Compounds: composed of two or more elements Halite NaCl (common table salt) Definition of a Mineral Definition of a Mineral • Naturally occurring • Inorganic* • Naturally occurring • Inorganic* * Carbon not in “organic” compounds formed primarily by biological processes Chain and ring hydrocarbons Amino acids Water H2O • • • • Solid Element or compound Definite chemical composition Regular (crystalline) internal structure Alcohols 2 Definition of a Mineral • Definite chemical composition • Regular (crystalline) internal structure Both diamond and graphite are pure carbon, but are distinct minerals Mineral Identification Habit (Geometry), often reflects internal crystal structure Cubic habit of halite Hexagonal habit of quartz Definition of a Mineral • Definite chemical composition • Regular (crystalline) internal structure Glass has an irregular internal structure, so is NOT a mineral Mineral Identification Hardness, also the result of crystal structure Talc: sheet structure Hardness 1 Corundum: 3D structure Hardness 9 3 Mineral Identification Mineral Identification Cleavage (how the mineral breaks), again reflects crystal structure! Density: depends on atomic weight of elements and tightness of packing in crystal structure Example of two cubic minerals: Galena and Halite Mica Platy cleavage Halite Cubic cleavage PbS density = 7.6 g/cm3 NaCl density = 2.2 g/cm3 Pb atomic weight = 207 S atomic weight = 32 Na atomic weight = 23 Cl atomic weight = 35 Mineral Identification Mineral Identification Magnetic Properties Minerals with iron (Fe) in the +3 and +2 state Magnetite: Fe3O4 Luster Metallic - pyrite Streak Color Earthy - limonite Vitreous (glassy) - quartz Hematite has a characteristic reddish brown streak 4 Major Mineral Groups Mineral Identification Sheet silicates e.g. mica Silicates: Si + O Solubility in Acid or Water Chain silicates Calcite fizzes when exposed to hydrochloric acid Quartz SiO2 Marble (made of calcite) weathers over time due to exposure to water Major Mineral Groups Silicates (all with Si and O) Aluminosilicates (felsic minerals) • Al + Ca, Na, K • Example: feldspar Ferromagnesian silicates (mafic minerals) • Fe, Mg • Example: olivine Major minerals (with quartz) of continental crust Major minerals of oceanic crust Framework silicates e.g. garnet Major Mineral Groups Nonsilicates Rockforming minerals • Calcite, dolomite • Carbonates, CO3 (limestone) • Halides (evaporites) • Halite, fluorite, silvite Cl, F, or I salts Accessory minerals • • • • • Native Elements Sulfides, S + metal Sulfates, SO4 Oxides, O + metal Hydroxides, OH + metal • • • • • Gold, copper, graphite Pyrite, galena Gypsum Magnetite, hematite Gibbsite (Al), goethite (Fe) 5
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