Characteristics and Properties MINERALS Characteristics and Properties

Mineral Characteristics What is a mineral? Naturally occurring Not man-made (synthetic) or biologically produced. 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)

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 Slow or quick cooling can determine the type of minerals formed.

Formation of Minerals --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.

Formation of 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

Uses of Minerals 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 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

Uses of Minerals 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

Mineral Characteristics Identifying Characteristics of Minerals Color Color by itself IS NOT sufficient to identify a mineral Luster How the material reflects light Metallic-shiny. Ex: silver, copper, etc Hardness How easily the mineral can be scratched Can be compared to the hardness of other minerals by using the Moh’s 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 Determined by the arrangement of the atoms Not all minerals have cleavage Density Ratio of mass to volume

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 Moh’s scale is a system of comparing the hardness of a list of 10 minerals. Developed by Frederich Mohs It lists them in order from 1 (softest) to 10 (hard) It gives a list of common objects and their hardness

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)