Geology mineral introduction to earth science

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Geology • What is a mineral? • What is a gem? • What is a rock? • How are these formed? • Edited from WARDS Geometry of Crystals Lab Mineral Criteria occurs naturally on Earth Mining: Dig for Diamonds Park is inorganically formed ( does not contain carbon) Exceptions are diamonds and graphite = pure carbon Criteria continued a solid at standard temp and pressure Elements that make up the substance are combined in fixed proportions The orderly arrangement of atoms that make up the substance produce a definite and repeating geometric pattern = characteristic crystal form Minerals Is an element (ex Gold, Au) or a compound (ex Quarts or pyrite FeS ) found naturally in rocks and soils There are more than 3500 minerals identified New minerals are being found every year Periodic Table • elements account for 98%of Earth’s crust • These elements combine to form minerals Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium Mineral Identification • Based on physical and chemical traits • Initially classified using one or more of the following physical properties • color specific gravity • luster cleavage or • hardness fracture • streak crystal form Color • Least reliable trait • Color can vary • Color can change when exposed to moisture, high or low temperatures or weathering Luster • Physical appearance of the unweathered surface • Way it reflects sunlight • Metallic or nonmetallic (glassy, pearly, silky, greasy or brilliant) Hardness • Is the resistance of a mineral’s smooth surface (face) to being scratched by a point or an edge • Mohs Hardness Scale has a range • (soft, easily scratched – ex Talc) to • 10 (hard – ex Diamond) • Any mineral can scratch a mineral with a lower hardness • Tools for Testing Hardness • You typically not carry around a supply of the 10 minerals on the hardness scale However, you can use the following items to help estimate the hardness of a mineral: • Finger Nail (H = 2.5) • Penny (H = 3) • Knife Blade (H = 5.5) • ar/L1.html Specific Gravity (Relative Density) • Specific gravity is the ratio of a mineral’s mass to the mass of an equal volume water • Very reliable Cleavage or Fracture Cleavage: a break along a smooth, flat plane producing smooth flat surfaces called faces Ex Galena Fracture: a break that is not smooth but produces irregular surfaces Ex Quarts Crystal Form • One of the most useful physical characteristics • Crystal forms result from the internal atomic arrangement of a mineral • Repetition of these arrangements results in crystal systems which produce the visible shape of the mineral Pyrite : “Fool’s Gold” • FeS2 • Is the result of many atoms of iron and sulfur forming a crystalline solid with a definite internal arrangement All crystals can be categorized into of crystal systems • As defined by axes • Axes are imaginary straight lines that pass through the center of the crystal faces at right angles to these faces and intersect at the center of a perfect crystal Isometric or Cubic Characteristics • equal exes intersecting at right angles to each other • Same measure • faces • Each face is a square • Angle between two adjacent sides is 90o • Ex Galena, halite, pyrite Hexagonal • Four axes • of the intersect at 60o angles to others in the same plane • 4th axis intersects the other at a 90o angle • Each of the similar faces join each other at 60o • more identical faces are different form the other • identical faces form 90o with the other • Ex Calcite, quartz and apatite Tetragonal • All axis intersect at 90o • of the axis are of equal length • Four identical often rectangular faces and two square faces • All adjacent faces hit at 90o • Ex Chalcopyrite, zircon Orthorhombic • axis intersect at 90o • None of the axis are equal length • Four of the faces form similar rectangles • of the other faces are similar rectangles but different from the first • All adjacent sides meet at 90o • Ex Olivine, silfur, topaz Monoclinic • axes none of equal length • Only axes intersect at 90o • identical or similar faces • identical faces unlike the first • sided prism • Faces meet at 90o and other angles • Ex Mica, gypsum, orthoclase, hornblende Triclinic • unequal axes • None of the axes intersect at 90o • Four similar or identical polygons and larger similar or identical polygons different form the first • None of the faces intersect at 90o • Ex feldspars Gems • A gemstone or gem, also called a precious or semiprecious stone, is a piece of attractive mineral, which — when cut and polished — is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value Rarity is another characteristic that lends value to a gemstone • Rocks (more info to come)  Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them These indicators separate rocks into igneous, sedimentary and metamorphic They are further classified according to particle size The transformation of one rock type to another is described by the geological model called the rock cycle • Mining
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