Minerals

Minerals: The Building Blocks of Life  A mineral must exhibit the following characteristics to be classified as such:  It must occur naturally  Solid at surface temperatures and pressures  Orderly internal structure (atoms arranged in a definite pattern)  Definite chemical composition that can vary within specified limits  Usually inorganic (some mineral formation can be mediated by biologic processes)  A rock is any solid mass of mineral matter that occurs naturally as part of our planet  Limestone is composed of impure masses of the mineral calcite  Granite is composed of aggregates of different minerals (quartz, hornblende, and orthoclase feldspar)  aggregate implies the minerals are joined in a way that retains the properties of each individual mineral  Some rocks are composed of non-mineral matter such as the volcanic rocks obsidian and pumice which contain noncrystalline glassy substances  Coal is composed of organic matter  Halite, composed of sodium and chloride (common salt) form a cubed shape internal structure which allows for salt crystals  Polymorphic minerals are minerals that share the same elements but have different properties:  Diamonds and Graphite both consist exclusively of carbon but have drastically different properties Property: Diamond: Graphite: Hardness 10 1 Cleavage* 4 directions 1 direction Lustre adamantine metallic Other High pressure needed Excellent lubricant *Cleavage is how a mineral breaks along planar surfaces  The carbon atoms in Diamond each are strongly bonded to 4 other carbons and form a 3D framework that accounts for the minerals hardness  The carbon atoms in Graphite share 3 bonds with other carbons, forming a layered sheet with strong bonds within a sheet but weak bonds between sheets  allows sheets to slide past each other easily, making the mineral a good lubricant  Physical properties of Mineral Identification include:  Shape: how a crystal grows (ie. Quartz forms well-developed hexagonal crystals with pyramid shaped ends)  Lustre: appearance/quality of light reflected (ie. metallic, non-metallic, pearly, glassy/vitreous, silky, resinous, earthy/dull)  Colour: minerals can have a single colour or multiple forms with varying colours (ie. Quartz can be purple in amethyst, pink in rose quartz, brown/black, or yellow/orange in citrine)  Streak: colour of a mineral in its powdered form or rubbed across unglazed porcelain (ie. reddish brown streak in Hematite is different than its colour)  Hardness: measure of resistance to abrasion/scratching using the Mohs scale  Cleavage: how a mineral breaks along planar surfaces, or areas of weak bonding  can occur at different angles, for example, calcite has 3 directions of cleavage not at 90°, fluorite has 4 directions, and amphibole has 2 not at 90°  Fracture: minerals with a consistent strength of bonds lack the ability to cleave along planar surfaces, and therefore break a certain way (ie. Quartz fractures to form smooth curves resembling a seashell, known as a conchoidal fracture)  most minerals fracture unevenly into irregular fragments  Specific Gravity: ratio of the weight of a mineral to the weight of an equal volume of water (heavier minerals have heavier specific gravity, such as Galena, which has a specific gravity of 7.5)  Other Properties: includes transparency (Calcite demonstrates double refraction), smell (sulfur-bearing minerals may smell like rotte