Chapter 2- Minerals Minerals - - Mineralogy: the study of minerals Minerals: naturally occurring, inorganic crystalline solid material with a specific chemical composition structure o Must exhibit the 5 following characteristics o Occur Naturally o Solid at surface temperature and pressures o Must possess an orderly internal structure; that is, its atoms must be arranged in a definite pattern o Must a have a chemical composition that can vary with specified limits o Usually inorganic (although mineral formation can, in some cases, be mediated by biological processes Rock: a consolidated mixture of minerals Composition of Minerals - Elements o The 4660 minerals are made of elements joined together in a consistent, repeating pattern - - o Defined by its unique combination of chemical composition and internal structure Atom: the smallest particle that exists as an element o Made of protons and neutrons o Electrons are what given the atoms bonding properties (through valence electrons) Polymorphs: two or more minerals that have the same chemical composition but different crystalline structures. They are exemplified by the diamond and graphite forms of carbon o Different because diamonds are formed under immense pressure 200km deep thus they have a compact structure o Graphite is form in low pressure and thus contains sheets of carbon with widely spread weakly held carbon atoms Bonding - - Ionic Bond: a chemical bond between two oppositely charged ions formed by the transfer of valence electrons from one atom to the other o Na+ + Cl- = sodium chloride o By giving up one electron, a neutral sodium atom becomes positively charged o By acquiring one electron, the neutral chlorine atom becomes negatively charges Covalent Bond: involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs o E.g. silicates Physical Properties of Minerals - - - Crystal Habit (Shape): the external appearance of mineral as determined by its internal arrangement of atoms Lustre: the appearance of quality of light reflected from the surface of the mineral o E.g metallic (pyrite) nonmetallic (quartz) vitreous (glassy as in the cases of quartz), pearl, earthy (dull), resinous Colour: light; by which otherwise identical objects can be differentiated Streak: the color of a mineral in powdered form o obtained by rubbing the mineral across a piece of unglazed porcelain known as a streak plate Hardness: minerals resistance to scratching and abrasion o Obtained using Mohs sale of relative hardness o Mohs Scale: a series of 10 minerals used as a standard in determining hardness - Cleavage: tendency of a mineral to break along planes of weak bonding o E.g micas have weak bonds in one planar direction, they cleave to form thin, flat sheets o Some show poor cleavage o Quartz have no cleavage at all - Fracture: any break of rupture in rock which no appreciable movement has taken place o Quartz breaks to form smooth curved surfaces resembling broken glass (conchoidal fracture) - - Specific Gravity: the ratio of a substances weight to the weight of an equal volume of water o If a mineral weights 3 times as much as the same volume of water, its specific gravity is 3 o Common to have 2.5-3 is a mineral weighs as much as a common rock o Galena, has is mined for lead has 7.5 Other Properties o Magnetism o Taste o Smell reaction HCL Mineral Classes - Silicates: any one of numerous minerals that have the silicon-oxygen tetrahedron as their basic structure o Every silicate mineral contains the elements oxygen and silicon o Silicon-oxygen tetrahedron: a pyramid shaped structure composed of 4 oxygen atoms surrounding a silicon atom that constitutes to the basic building block of silicate elements o (SiO4)4o These tetrahedrons can like with other tetrahedrons forming single chains, double chains or sheet structures Common Silicate Minerals - - - - - - - - Ferromagnesian (Dark) Silicates: silicate minerals that contain ions of iron or magnesium (or both) in their structure. They are dark in color and have higher specific gravity than nonferromagnesian silicates o E.g olivine, pyroxenes, amphiboles, dark mica( biotite), dark garnet Olivine o Higher temperature silicate, black to olive in color, glassy lustre and conchoidal fracture o Silicone oxygen tetrahedron bonded to magnesium and iron o No consistent plane of weakness; so no cleavage o Forms rounded, small crystals Pyroxenes o Important components of igneous rock o 2 planes of cleavage at 90 degrees o Single chains of tetrahedrons bonded to magnesium and iron o Augite, dominant in basalt which is common in oceanic and volcanic areas Amphibole o Hornblende; dark green to black, 2 planes of cleavage at 60 and 120 degrees o Fracture at ionic bonds between silica chanins which is weaker than colvalent bonds between the silica o Due to double chains the planes of weakness intersect as a wider angle (120 degrees) Biotite o Dark iron rich member of mica family o Sheet cleavage (one plane) o Biotite has shiny black appearance, that helps it distinguish from other dark ferromagnesian minerals o Common component of igneous rocks Garnet o Similar to olivine as its strucuture is composed of tetrahedrons linked by metallic ions o Like olivine has glassy lustre, lacks cleavage, possesses conchoidal fracture o Colors are varied; usually brown or deep red Non-Ferromagnesium (Light) Silicates: silicate minerals that lack iron or magnesium. They are generally lighter in colour and have lower specific gravity than dark silicates Muscovite: o Mica family, light in color, pealy lustre o Has excellent cleavage in one direction (sheets) o Transparent- translucent in sheets o Very chiny and gives a distinct sparkle (e.g sparkle in sand) Feldspar o Most common mineral group, can form under wider range of termperatures and pressures o 2 planes of cleavage at 90 degrees, 6 on Mohs scale o Lustre ranges from pearly to glassy o o - - Quartz o o o o o Clay o o o o o o o As one component in a rock, they can be identified by their rectangular shape and smooth, shiny faces 2 different feldspar exists: Orthoclase and Plagioclase feldspar o Orthoclase is a type of feldspar that contains potassium ions (thus called potassium feldspar) Lighter in color, usually creamy or salmon pink o Plagioclase feldspar contains both calcium and sodium ions that can freely substitute for each other during crystallization Greyish to blue-green in color o To differentiate, look for scratch like lines called striations that are commonly present on cleavage planes of plagioclase feldspar but absent on orthoclase feldspar only common silicate that consists entirely of oxygen and silicon contain two O2- for every one Si2+ pure quartz is colorless and clear can form hexagonal crystals with pyramid shaped ends common varieties include, milky, smoky, rose amethyst (purple) A term used to describe a variety of complex minerals that, like micas have a sheet structure Very fine-grained and studies microscopically Originate as products of chemical weathering or other silicates (mostly feldspars) Make up large percentage of soil Kaolinite is a common clay used in the manufacturing of fine chinaware and high gloss paper Some clays soak water allowing them swell to several times their size Used in cat litter and additives for milkshake Important Non-Silicate Minerals - - Carbonate o Calcite and dolomite o Both have vitreous lustre, hardness of 3-4, rhombic cleavage (in 3 directions, not 90 degrees) o Calcite reacts to HCL Halides o halite, sylvite and gypsum o thick layers found in ancient seas and saline lakes o halite= salt, sylvite=principal mineral for potash, gypsum =plaster
