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MINERALS Characteristics and Properties Mineral Characteristics • What is a mineral? • – Naturally occuring • Not man-made (synthetic) or biologically produced. – Pearls, styrofoam, charcoal are not minerals – Inorganic • Not formed from processes involving organisms (living or once living) – Solid – Has definite chemical composition • An element or compound – Has an orderly arrangement of atoms • Crystalline structure-that is-atoms have repetitive patterns and internal structures are distinct. • Geometric solids with smooth surfaces (crystal faces) Identifying Characteristics of Minerals – Color • – Color by itself IS NOT sufficient to identify a mineral Luster • How the material reflects light – – – Hardness • • – How easily the mineral can be scratched Can be compared to the hardness of other minerals by using the Mohs scale Streak • – The powder form of the mineral left on a porcelain plate (must be softer than the porcelain) Cleavage • The way the mineral splits along flat surfaces – – – Metallic-shiny. Ex: silver, copper, etc Nonmetallic-Pearly or vitreous. Determined by the arrangement of the atoms Not all minerals have cleavage Density • Ratio of mass to volume – Determined by the mass of the atoms and how close they are Formation of Minerals • How are minerals formed? – One way is the cooling of magma • • • • • Thermal energy is lost; atoms migrate together and form different compounds The elements present and the amounts determine the kind of minerals Different crystal structures are formed If the magma cools slowly, large crystals are formed. Different minerals form at different temperatures. Heavier minerals such as magnetite sink and lighter ones float. Minerals such as quartz and calcite form late in the cooling process and are known as hydrothermal minerals. In the last few years, hydrothermal vents have been formed on the ocean floor. In these areas, sea water filters into the hot crust and is heated to 400 degrees C. The hot water then reacts with the crust and becomes a metal bearing liquid. When it returns to the cooler sea floor, it deposits minerals, including iron, copper and zinc sulfide. --Minerals can precipitate out of a solution When water is saturated with dissolved solids and can’t hold any more, the excess falls out of the solution. An example of this is the manganese nodules on the ocean floor --Minerals can form by evaporation • Minerals such as salt, gypsum and calcite (calcite forms in two ways) are formed from sea water when it evaporates. This happens in warmer parts of the world where the sun's heat evaporates the water and leaves the minerals. Other ways that minerals are formed: – Some minerals are formed from the weathering of rocks. • Chemical changes are caused by atmospheric oxygen, water and acid rain. Such action can change feldspars to kaolin and pyrite (fools gold) into a brown iron ore called limonite – And lastly some minerals are formed when rocks are metamorphosed, that is subjected to heat and pressure. • Minerals formed in this way include garnet and mica. Mineral Groups • Minerals that contain oxygen and silicon are called “silicates”. These two minerals combine to form most of the minerals in the earth’s crust. • They are the most abundant single minerals in the earth’s crust (oxygen-46.6%; silicon-27.7%) • More than half of the minerals in the earth’s crust are feldspars which is a silicate • Some other examples of silicates include: talc, quartz, mica, topaz, hornblende, garnet, zircon • Uses of Minerals Gems – Rarity and beauty makes them valuable – Gemstones used for jewelry are cut and polished and sometimes don’t resemble the raw form of the mineral • May have a crystal structure that allows it to be cut in facets • May have the addition of another mineral that gives it a brighter color • Ores – A mineral is an ore if it contains a substance that can be sold for profit • • • • Hematite is the ore of iron Bauxite is the ore of aluminum Copper comes from chalcopyrite ore Rutile is the ore that titanium comes from – Titanium is valuable because of its strength and low density (lightness) – Ore deposits are formed when fluids travel through weaknesses in rocks, such as fractures and cracks. – The minerals dissolved in the fluids are left behind when the liquid evaporates, forming “vein deposits • Mining – Ores are only profitable if the cost of mining them is less than the value of the material being mined • Waste rock has to be removed • This can be expensive and harmful to the environment Physical Appearance • Color cannot be used exclusively to identify minerals. For example the color of turquoise can vary from blue to green • Minerals may have varying degrees of transparency, which is the ability of light to pass through a substance—quartz can be transparent, but can contain flaws that make it translucent. This is related to Luster. • Luster is definitely an identifying physical characteristic • It describes how light reflects from the surface of the mineral. Describers might include: – Metallic, waxy, pearly, earthy, dull, glassy (vitreous), silky Hardness • This is how easily a mineral can be scratched and is definitely an identifying characteristics. In order to be scratched by an object, the mineral must be softer than the object doing the scratching. • The Mohs scale is a system of comparing the hardness of a list of 10 minerals (The Giant Cat Found a Foolish Quail that Couldn’t Dance) – Developed by Frederich Mohs – It lists them in order from 1 (softest) to 10 – It gives a list of common objects and their hardness • If the mineral scratches the common object but the object won’t scratch the mineral, the mineral is the hardest • Moh's Scale Streak • Streak is the color of the powder form of the mineral • A streak plate is used to do this test. It is a piece of unglazed porcelain—which has a hardness of 7 on the Moh’s scale. A streak of the mineral is left on the porcelain when it is rubbed across with the mineral. The mineral must be softer than the streak plate if this is to work. • Some minerals leave a certain color streak, which is an identifying characteristic. – An example of this is hematite, which although it is a black mineral, leaves a red streak Cleavage and Fracture • When a mineral breaks it does so either by fracturing or by cleaving. Crystal cleavage is a smooth break producing what appears to be a flat crystal face. Here are a few rules about cleavage. First cleavage is reproducible, meaning that a crystal can be broken along the same parallel plane over and over again. All cleavage must parallel a possible crystal face. • Fracture describes the way a mineral breaks and is different from cleavage. A fracture might be splintery, conchoidal (like glass) , jagged or earthy (like a ball of clay) Common Minerals • There are more than 4000 named minerals, but most rocks are made up of just a small number—these are the “rock forming” minerals • Central Florida is the heart of the US phosphate industry and the leading producer of phosphate in the world. Phosphate is used to make fertilizer – Phosphate is a profitable industry in Florida – Mining for phosphate also produces toxic substances such as uranium and arsenic because the phosphate is buried under these substances. The by-products can’t be returned to the mine because they are a source of pollution