Minerals


 * Rock forming minerals

minerals from magma** the type & number of elements in the magma determine which minerals will. the rate at which magma cools determines the size of mineral crystals. small crystals form from rapidly cooling magma, and large crystals form from slowly cooling magma.
 * minerals from soloutions** a liquid is saturated when it becomes full of a dissolved substance and can dissolve no more of that substance. if more of the substance is added to a saturated soloution, it is called supersaturated, and mineral crysralsform into solids from the soloution.minerals that form from the evaporation of the liquid in which they were dissolved are called evaporites.
 * identifying minerals** geoligists identify minerals using tests based on a minerals physical and chemical properties, such as crystal form, luster, hardness, cleavage, fracture, streak, color, specific gravity, texture density and special properties.
 * crystal form** some minerals form such distinct crystal shapes that they are immediately recognizable. however perfect crystals are not always formed so identification


 * luster** the way that a mineral reflects light from its surface is called luster. there are 2 types of luster: metallic luster and nonmetallic luster. luster should usually be used in combination other physical chara. to identify a mineral.

hardness of 10 easily recognized that with the exception of diamond readily found in nature. that break with rough arclike or jagged edges because of their tightly bonded atoms are said to have fracture. Streak is the color of a mineral when it is broken up and powdered. The streak test, which typically involves rubbing the mineral against an unglazed porcelain plate, is most useful in identifying metallic minerals. It can be used only on minerals that are softer that the porcelain plate. Color is one of the most noticeable characteristics of a mineral. It is also one of the least reliable clues of a mineral’s identity. Several special properties of minerals can also be used for identification purposes. Some of these properties are magnetism, striations, double refraction, effervesance with hydrochloric acid, and fluorescence. Texture describes how a mineral feels to the touch, and like luster, it is subjective. It is often used in combination with other tests to identify a mineral. Two minerals of the same size may have different weights due to a difference in density. Density reflects the atomic mass and structure of a mineral. Density is expressed where D= density, m=mass and v= volume. Because density is not dependent on the size or a shape of a mineral, it is a useful identification tool. The most common measure of density used by geologists is specific gravity, the ratio of the mass of a substance to the mass of an equal volume of water 4 degrees Celsius. In order to study the may minerals on earth and understand their properties, geologists have classified them into groups. Each group has a distinct chemical nature and specific characteristics. Minerals that contain silicon and oxygen, and usually one or more other elements, are known as silicates. Silicates make up approximately 96 percent of the minerals present in Earth’s crust. The basic building block of the silicates is the silica tetrahedron. A tetrahedron, (plural, tetrahedral) is three- dimensional shape that resembles a pyramid. Because silicon atoms have four valence electrons, they can bond with four oxygen atoms. Individual tetrahedron ions are strong and can bond together to form sheets, chains and complex three-dimensional structures. The bonds between the atoms help determine several mineral properties, including cleavage or fracture. The tetrahedron formed by silicates contains four oxygen ions bonded to a central silicon atom. Chains, sheets, and complex structures form as the tetrahedral bond with other tetrahedral. These structures become the numerous silicate minerals that are present on Earth. Carbonates are minerals composed of one or more metallic elements and the carbonate ion. Oxides are compounds of oxygen and a metal, such as hematite. Sulfides are compounds of sulfur and one or more elements, such as pyrite. Sulfates are compounds of elements with the sulfate ion, such as anhydrite. Halides are made up of chloride or fluoride along with calcium, sodium, or potassium such as halite. Native elements are made up of one element only, such as silver. Minerals are used to make computers, cars, televisions, desks, roads, buildings, jewelry, beds, paints, sport equipment, medicines, and many other things. A mineral is an ore if it contains a useful substance that can be mined at a profit. The classification of a mineral as an ore can change if the supply of or demand for that mineral changes. Ores that are located deep within Earth’s crust are removed by underground mining. Those near Earth’s surface are obtained from large, open-pit mines. The removal of unwanted rock and dirt from mining can be expensive and harmful to the environment. Gems are valuable minerals that are prized for their rarity and beauty. Gems such as rubies, emeralds and diamonds are cut, polished and used for jewelry. Lava is magma that out onto Earth’s surface. Igneous rocks form when lava or magma cools and minerals crystallize. The type of igneous rock that forms depends on the composition of the magma, which is often a slushy mix of molten rock, dissolved gases and mineral crystals. Magma is classified as basaltic, andesitic or rhyolitic based on the amount of silica it contains. Silica affects melting temperature and impacts how quickly magma flows. The four main factors involved in the formation of magma are temperature, pressure, water content and mineral content. Temperature generally increases with depth in Earth’s crust. This temperature increase is known as the geothermal gradient. Pressure also increases with depth as a result of the weight of overlying rock. The increased pressure on a rock also increases the rock’s melting point. Rocks and minerals often contain small percentages of water, which changes the melting point of the rocks. As water content increases, the melting point decreases. Rocks melt at lower or higher temperatures because their component minerals have lower or higher melting points in general, rocks that are rich in iron and magnesium melt at higher temperatures than rocks that contain higher levels of silicon. The process whereby some minerals melt at relatively low temperatures while other minerals remain solid is called partial melting. If temperatures are not high enough to melt the entire rock, the resulting magma will have a different composition than that of the original rock. When magma cools, the first minerals that crystalline are the last minerals that melted during partial melting. This process is called fractional crystallization. In the basaltic intrusion of the Palisade Sills in the Hudson River valley of New York and New Jersey, small crystals formed in the chill zone as the outer areas of the intrusion cooled more quickly than the interior. Under certain conditions, newly formed crystals can be removed from magma, ending the chemical reactions between the magma and the minerals. When magma cools and crystallizes below Earth’s surface, intrusive rocks form. Magma that cools and crystallizes on Earth’s surface form extrusive rocks. Igneous rocks are classified by their mineral compositions. Basaltic rocks are dark- colored, have lower silica contents, and contain mostly plagioclase and pyroxene. Granitic rocks are light- colored, have silica contents, and contain mostly quartz, potassium feldspar, and plagioclase feldspar. Rocks have a composition of minerals that is somewhere between basaltic and granitic are called intermediate rocks. At fourth category, called ultrabasic contains the rock peridotite. Ultrabasic rocks contain only iron- rich minerals such as olivine and pyroxene and are always dark. Rock type can be determined by estimating relative percentage of minerals in the rocks. Texture refers to the size, shape, and distribution of the crystals or grains that make up a rock. When lava flows on Earth’s surface, it cools quickly and there is not enough time for large crystals to form. The resulting extrusive igneous rocks have crystals so small that they cannot be seen without magnification. When lava cools so quickly that crystals do not form, volcanic glass is the result. When magma coos slowly below Earth’s surface, there is sufficient time for large crystals to form. Thus, intrusive rocks can have crystals larger than 1cm. A poryphyritic rock is characterized by large, well- formed crystals surrounded by finer- grained crystals of the same mineral or different minerals. The spongy appearance that results from gas bubbles trapped in lava is called vesicular texture. Scientists use a special microscope, called a petrographic microscope, to help them identify minerals by examining the mineral grains in sections of rock thin enough for light to pass through. Valuable ore deposits often occur within igneous intrusions. At other times, they may occur as veins in the rocks surrounding intrusions. Veins of extremely large- grained minerals that can contain ores are called pegmatites. Diamonds and other minerals that can form only under very high pressure are found in rare, ultrabasic rocks known as Kimberlites. The interlocking grain textures and the resistance to weathering of many of the minerals present in igneous rocks make them especially useful as building materials**.**
 * Hardness** hardness is a measure of how easily a mineral can be scratched. German geologists friedrich mohs developed a scale by which an unknown minerals
 * cleavage** and fracture a mineral that splits easily and evenly along 1 or more planes of weak atomic bonds is said to have cleavage. to identify a mineral based on its cleavage goes. count the # of cleaved planes and study the angle or angles between them. minerals
 * Streak**
 * Color**
 * Special properties**
 * Texture**
 * Density and specific gravity**
 * Mineral groups**
 * Silicates**
 * Visualizing the Silica Tetrahedron**
 * Carbonates**
 * Oxides**
 * Other groups**
 * Economic Minerals**
 * Ores**
 * Gems**
 * Igneous Rock Formation**
 * Composition of magma**
 * Magma formation**
 * Magma formation**
 * Partial melting**
 * Fractional Crystallization**
 * Visualizing Fractional Crystallization and Crystal Settling**
 * Fractional Crystallization**
 * Mineral composition of Igneous Rocks**
 * Texture**
 * Crystal** **size and cooling rates**
 * Crystal** **size and cooling rates**
 * Porphyritic rocks**
 * Vesicular rocks**
 * Thin sections**
 * Veins**
 * Pegmatites**
 * Kimberlites**
 * Igneous rocks in construction**