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What is a Mineral?

What is a Mineral?
What is a Mineral A naturally occurring, inorganic solid that has a definite chemical composition and/or crystal structure Formation Composition • Minerals come from cooled magma • 2500 kinds of minerals; some are easy to find and others are rare. • Mineral Properties Each type of mineral has its own combination of properties that identify it. Some of the properties are Color Many minerals come in a wide variety of colors. Different minerals can be the same color. It is difficult to use just color to identify a mineral. Streak Streak is the color of a mineral in powdered form. You can see a mineral’s streak by rubbing a sample across an unglazed ceramic plate and observing the powder left behind. Sometimes a mineral’s streak is very different from the color of the sample. Hardness Hardness is the resistance of a mineral to scratching. Geologists use the Mohs' hardness scale to seriate and compare mineral hardness. Specific gravity Specific gravity is the ratio of the weight of a given volume of a mineral to the weight of an equal volume of water. Higher specific gravity means the mineral is heavier. Cleavage Cleavage is how a mineral breaks. Some minerals break in smooth, flat surfaces at identifiable angles, such as calcite. Others fracture and produce no flat surfaces, such as quartz. Fracture Fracture is how a mineral breaks when no cleavage surfaces form. For example, quartz breaks in a pattern known as conchoidal fracture. Conchoidal fracture looks like smooth, curved surfaces. Luster Luster is how a mineral reflects light or how it shines. Some ways to describe luster include glassy or vitreous, metallic, dull, and pearly. Crystal form Crystal form describes the geometric shape of a crystal. There are seven main groups of crystal shapes, including cubic, hexagonal, and tetrahedral. Transparency Transparency describes how a mineral transmits light. Some minerals are transparent (you can see through them); others are translucent (some light passes through a sample) or opaque (no light passes through a sample). Magnetism Magnetism is a special property of some minerals, especially magnetite. Samples are attracted by a magnet. Lodestone, a special form of magnetite, is a magnet itself. Reaction to acid Some minerals react to acid. Calcite especially will fizz and bubble when it comes in contact with an acid such as hydrochloric acid at room temperature. Identifying Minerals • Physical Properties are used to identify minerals: – Color always a reliable way to identify minerals. – However, color can change do to pollution, heat, and cold Types • Idiochromatics:Fairly constant colour(Copper Group of minerals) • Allochromatic: Variable colour due to impurities(Mineral Like Quartz, Calcite, Fluorite) • Pseudochromatic: Showing a false colour Simultaneous reflection and refraction(Diamond) LUSTER: • The way a • mineral reflects • light from • its surface • Non metallic luster: – Don’t have much of a reflection; known as glassy, pearly, and dull Factors affects Lustre ` The refractive index of a mineral • The absorption (of light) capacity of a minerals • The nature of reflecting surface   Metallic: Shine resembles as of MetalsGalena  Vitreous: Lustre of GlassQuartz   Pearly: Shine resembles as of Pearl Labradorite   Silky: Shine resembles as of Pure silkGypsum   Resinous: oily shine, waxy or greasyNepheline   Dull: Shine is almost absentChalk. Clay , Bauxite Streak • Color of powder scraped off when it is rubbed against • a hard, rough surface • Streak may be a different color than the mineral itself. Streak: colour of the fine powdered mineral Determined by using a streak plate Magnetite and chromite are almost black in colour where as streak of magnetite is black and that of Magnetite is brown Hardness • The ability to resist being scratched • Most useful properties for identifying a mineral • Numbered 110. – 1Talcsoftest – 10Diamond hardneest Cleavage Fracture • Describe how the mineral breaks along flat surfaces. Ex: Halite • Most minerals break along a rough or jagged surface. Ex: Quartz Fracture Splintry: Rough • Even: Broken srface is • woody smoothChert fractureKyanite Uneven: Broken surface Hackly:Irregular sharp • • fine projections is irregular surface Native Fluorite copper • Conchoidal: Broken • Earthy: Surface is surface is having smooth and soft and concentric rings with porousChalk faint outlineQuartz Tenacity (Behaviour towards Break, bend, cut or crush) • Sectile: Cut with a knife • Malleable: Can be flattened by a hammer • Brittleness: Change to fine grain or powder under a knife or a hammer Crystal Shape • Minerals have a crystal shape that results from the way the atoms or molecules come together as the mineral is forming Structure of a Mineral (Physical make up of a mineral) • Tabular: Mineral in the form of flattened, square, rectangle (Calcite, orthoclase, barite) • Elongated: Mineral is in the form of a thin or thick elongated, columnlike crystals. (Beryl, Quartz, Hornblende) • Bladed: Mineral appears to be composed of thin, flat , bladed like overlapping. (Kyanite) • Lamellar: Mineral made up of relatively thick, flexible, leaflike sheets.(Vermiculite) • Foliated: similar to lamellar in boarder sense but individual sheets are thin. (Muscovite) • Fibrous: Mineral composed of Fibres, generally separable easily or with a little difficulty. (Asbestos Gypsum) • Radiated: needle like crystal appears to originating from a common point. (iron pyrite) • Granular: densely packed mass of small crystal grains(Chromite) • Globular: Botroiydal, rounded, bulblike overlapping, (Hematite) • Reniform: Globular similar to human kidney shape(H) • Mammillary: Globular form, conspicuous overlapping with each other(malachite) Special Properties • Magnetite: Naturally magnetic • Halite: Tastes salty Sulfur: Smells like rotten eggs 13.3: Uses of Minerals • Minerals are raw materials used for a wide variety of products from dyes to dishes and from table salt to televisions Some minerals Quartz Feldspar Fluorite Magnetite Hornblende Gypsum Calcite Biotite Copper Hematite GROUPS • Silicate • Pyroxene • Amphibole • Mica • Feldspar • olivine • Alpha Quartz or High Quartz (describes Physical Properties of Quartz stable at normal room conditions Clear Quartz Environment : develops in a wide variety of environments, igneous, metamorphic, Hardness: 7.0 on Moh's hydrothermal Scale Index of refraction: • 1.5441.553 Transparency: Transparent to opaque Luster: Most specimens have a vitreous Birefringence: luster; Some yellow or brown are resinous; 0.009 Streak: White Earthy specimens are dull; Very rare varieties Spec. Grav.: 2.5 2.7 have an adamantine luster Crystal: Hexagonal Other Marks for identification purposes: (prisms, pyramidal) Many specimens fluoresce; All specimens are triboluminescent and piezoelectric Fracture: Conchoidal Striking Features: Hardness, crystal forms, Cleavage : none striations on crystal faces, and frequent Tenacity: Brittle appearance of conchoidal fractures on crystal faces. In Group: Silicates; Complex Tests: Dissolves in hydrofluoric acid Tectosiliates; Silica Group: Distinguishing from Similar Minerals: Beryl is or as an oxide by a few harder (7½ 8), without the horizontal references striations of Quartz; Feldspar is a softer stone Other Names: Silica (6), with perfect cleavage; Calcite is very soft (3) (describes Typical Cutting StylesFaceted, cabochons Quartz, Chalcedony, and Opal) Varieties of Quartz Other than Clear Quartz, Quartz occurs as Amethyst, Aventurine, Citrine, Carnelian, Herkimer Diamonds, Jasper, Onyx, Rose Quartz, Rutilated Quartz, Smoky Quartz and Tourmalinated Herkimer Diamonds are Quartz crystals with double terminations and Tourmalinated Quartz contains hairs of Tourmaline crystals, but both are minor Quartz family members. Quartz Calcite Comments: Purplecolored druse of amethystine quartz and white calcite. Location: Rio Grande do Sul, Brazil. Scale: Sample size 20 cm. Quartz Chalcopyrite Comments: Wellformed crystals of chalcopyrite and quartz. Location: Boldut mine, 61 level (350 meters deep), Cavnic, Maramures, Rumania. Scale: 5.5 x 3.5 cm. Quartz Ilvaite Comments: Black, prismatic ilvaite with quartz. Location: First Sovietskij mine, Dalnjegorsk, Russia. Scale: 3.5 x 4.5 cm. Images: Quartz Comments: Crystal druse of transparent quartz crystals. Location: Hot Springs, Arkansas, USA. Scale: Specimen size 6 cm. Images: Quartz Apatite(CaF) Comments: Purple crystal of fluorapatite on slightly smoky quartz crystals. Former Dr. E.E. David and Houston Museum collections. Location: Pech, Kunar Province, Nuristan, Afghanistan. Scale: Crystal size 3.0 x 2.1 x 1.7 cm. Images: Quartz Epistilbite Comments: White epistilbite cluster 25 mm across on amethyst quartz crystal matrix. Location: Sawda, Jalgaon, Maharashtra, India. Scale: 10x8x5 cm. Images: Quartz Comments: Slightly smokey quartz overgrown with rose quartz. Note the exceptional transparency of the rose quartz. Location: Lavra da Ilha, Taquaral, Minas Gerais, Brazil. Scale: 10 cm by 5.2 cm. Feldspar • KAlSi O 3 8 Orthoclase KAlSi O 3 8 Microcline NaAlSi O CaAl Si O Plagioclase 3 8 2 2 8 In the manufacture of highclass, colourless glass, feldspar should have a maximum of 0.1 Fe O though upto 0.3 is 2 3 permissible. Colour • Orthoclase usually light colored white, pink, yellow, or cream, and not transparent. The gem variety is clear to pale yellow, and some called "noble orthoclase" Microcline white, pink, pale yellow, or sometimes greenblue, and not transparent. The greenblue variety is called "amazonite" Plagioclase gray to grayishwhite is common, but may also be white, pink or pale yellow. More semi opaque than the other feldspars on average, and contains striations on some crystal faces or cleavage surfaces. • Hardness 66.5 Environment The feldspars make up the major constituent of many igneous and metamorphic rocks, they form at medium to high temperature and at some depth. Microcline can form in granite pegmatites and at lower temperatures. Associated Quartz Other feldspars Hornblende • Luster: vitreous to semi vitreous. • Sp. Gravity:2.562.58 • Cleavage: 2sets • Varities: Adularia transparent varieties. » Sanidine ahigh temperature variety(stable over 900 ˚C) • Composition: K Al Si O 3 8 classification • Potash feldspar: » Orthoclase » Sanidine » microcline • Sodalimefeldspar: » Albite labradorite » Oligoclase Bytwonite » Andesine anorthite • Crystallographically: • monoclinic » Orthoclase » Sanidine Triclinic Microcline Albiteanorthite Feldspar is generally used for three purposes In making the body composition of several types of procelain, china and earthenware and also in the preparation of glazes and enamel. As an important ingredient in the glass sand batch. As a bonding agent in the manufacture of bonded abrasives like wheels and discs of garnet, corundum, emery etc. The glass and ceramic industries are the major consumers of feldspar and account for 95 of the total consumption. Feldspar is used in varying proportions in porcelain, china and earthenware. Earthenware contains on an average 12 feldspar 25 ball clay 28 chinaclay 35 quartz This proportion of feldspar varies in different products like Wall tile 5 Floor tile 30 Statutory porcelain 50 Sanitary china and prodelain bodies 30