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Transcript of ScienceCh9RocksAndMinerals
Minerals I. Minerals A. The study of minerals 1. Minerals defined a) A solid element or compound found naturally in the earth and having a crystalline structure b) Includes elements and compounds but not mixtures; have definite chemical and physical properties Quartz crystal 2. Mineralogy--the science of studying, classifying, and identifying minerals 3. Occurence of minerals a) Most common elements in the earth's crust--oxygen, silicon, aluminum, and iron b) Most minerals exist as chemical compounds 4. General classifications of minerals a) Native elements--those minerals found uncombined with other elements Native gold, silver, and copper b) Halides--minerals that are compounds consisting of halogens Halite Fluorite c) Sulfides--mineral compounds consisting of sulfur Pyrite ("fool's gold") Galena Cinnabar d) Oxides--mineral compounds consisting of oxygen Magnetite Cuprite e) Carbonates--mineral compounds consisting of the carbonate ion Dolomite Calcite f) Silicates--minerals that are compounds consisting of silicon and oxygen; the largest group of minerals Asbestos Quartz 5. Structure of minerals a) Found in the form of crystals--a solid substance of atoms arranged in a definite geometric order b) Characterized by flat-faced surfaces known as crystal faces c) 6 crystal shapes--isometric, tetragonal, orthorhombic, monoclinic, triclinic, and hexagonal d) A mineral can be identified by its crystal shape Both graphite and diamond are forms of carbon, but they have different crystal structures. e) Law of interfacial angles--the angles between a crystal's corresponding faces are always the same B. Characteristics used to identify minerals 1. Surface color 2. Streak color a) The color of a mineral's powder b) Can be used to identify a mineral by doing a streak test on a streak plate 3. Luster a) How light is reflected from the mineral's surface; the shininess of a mineral b) Classified as metallic and nonmetallic luster 4. Hardness a) How well a mineral resists being scratched b) Harder substances scratch softer substances. c) Mohs scale of hardness--rates the relative hardness of substances on a scale of 1 to 10 d) The hardest substance--diamond Talc is easily scratched with a coin or even a fingernail. 5. Cleavage and fracture a) Cleavage--how a mineral may break along flat surfaces making fragments with the same shape b) Fractures--a break that does not produce fragments like the original Conchoidal fracture of obsidian Fibrous fracture of asbestos Mica breaks off into thin sheets. 6. Specific gravity--a ratio of the mineral's density to the density of water (1.00 g/cm ) 3 7. Other properties a) Testing the mineral to see if it reacts with acid by releasing gas (effervescence) b) Testing the mineral for fluorescence, phosphorescence, and radioactivity Fluorescent minerals C. Valuable minerals 1. Common, useful metals a) Not often found as the pure element but combined with mineral in an ore Iron ore b) Iron--most commonly used; alloys of iron and carbon form steel c) Copper--excellent conductor of electricity; alloys include brass and bronze d) Aluminum--most abundant metal of the earth's crust; a light, strong metal Bauxite (aluminum ore) e) Others--lead, nickel, tin, zinc, and uranium 2. Precious metals a) Called precious for their rarity and beauty b) Gold c) Silver--most reflective metal; best conductor of heat and electricity d) Platinum 3. Precious stones a) Rare, beautiful, durable mineral crystals b) Diamond--hardest mineral substance; along with graphite, it is a crystal form of carbon c) Ruby--form of corundum that gets its red color from chromium Star ruby Pigeon-blood ruby d) Sapphire--form of corundum that gets its blue color from iron or titanium Star sapphire e) Emerald--a form of beryl that gets its green color from chromium oxide Different variations of beryl, including 1. golden beryl crystal, 2. heliodore. 3. emerald, 4. aquamarine, 5. morganite f) Aquamarine--a form of beryl that gets its blue-green color from iron oxide 4. Semiprecious stones a) Not as rare, durable, or valued as precious stones b) Often confused with precious stones c) Include red spinel, amethyst, zircon, tourmaline, opal, lapis lazuli, turquoise, chalcedony, and jade II. Rocks A. Introduction 1. Rock defined a) The building blocks of the earth's crust b) An aggregate of mineral matter making up the earth's crust 2. The difference between rocks and minerals--rocks are often mixtures of many minerals; minerals are either elements or compounds B. Igneous rocks ("made by fire") 1. Rocks formed from hardened magma a) Intrusive rock--magma that hardens underground b) Extrusive rock--magma that hardens above the surface 2. Classified according to texture a) Texture--the look and feel of the rock; refers to the size of the rock's mineral grains b) Determined by how fast the rock cooled c) A coarser texture produced by the presence of more and larger mineral crystals; a smoother texture produced by an amorphous composition d) Many igneous rocks have the same chemical composition but a different texture. Both granite and obsidian have the same chemical composition. 3. Coarse-grained igneous rock a) Intrusive rock with larger mineral crystals formed by slower cooling b) Granite--the most common igneous rock c) Gabbro--dense rock of the lower crust 4. Fine-grained igneous rock a) Extrusive rock with smaller mineral crystals formed by quicker cooling b) Examples: rhyolite and basalt 5. Mixed-textured rock a) Cools slowly at first and then quickly b) Also known as porphyritic rock 6. Smooth-textured rock a) Cools very quickly; has an amorphous structure because no crystals are formed b) Example: obsidian ("volcanic glass") 7. Porous rock a) Hardens as gases escape; forms a lightweight rock b) Examples: pumice and scoria C. Sedimentary rocks ("deposited by water") 1. Rocks formed from the cementing of sediments--rocks and particles of rocks deposited by water 2. Mechanical sediments a) Formed when sediments are transported and deposited elsewhere by the water, wind, or ice b) Rocks produced from mechanical sediments--shale, sandstone, conglomerate rock, and breccia c) Shale--most common sedimentary rock; can be split into thin layers d) Sandstone--rocks formed from grains of sand fused together e) Conglomerate rock and breccia--types of rock that contain rock fragments mixed with sand and cemented together Conglomerate rock Breccia 3. Chemical sediments a) Formed from dissolved minerals that precipitate out of water or formed when water evaporates leaving behind the sediments (evaporites) b) Includes salt deposits and gypsum deposits Salt deposits along the Dead Sea 4. Organic sediments a) Composed entirely of fossil material b) Limestone--formed from shell fragments; composed primarily of calcium carbonate c) Includes coal (a fossil fuel) A fossil set in limestone 5. Types of coal a) Anthracite--highest quality b) Bituminous--most common form c) Lignite--lowest quality 6. Sedimentary rock contains concretions--hard, round structures that form when dissolved minerals crystallize around a nucleus 7. Layers of sedimentary rocks a) Arranged into layers or beds of rock known as strata b) Law of superposition--strata are in the order in which they were laid down c) Most strata were probably laid down quickly by the Flood. D. Metamorphic rocks ("changed in form") 1. Any type of rock (sedimentary, igneous, or metamorphic) that has been changed into a new type of rock by heat or pressure 2. Types of metamorphism a) Contact--a change that is caused by contact with hot magma b) Regional--a change that is caused by the heat and pressure that occurs when rocks are folded or faulted 3. Foliated rocks a) Metamorphic rocks made up of leaflike layers b) Examples: slate, gneiss, schist, and phylite Slate is metamorphosed shale. 4. Unfoliated rocks a) Metamorphic rocks that cannot be split into layers b) Includes marble (metamorphosed limestone or dolomite) c) Other examples: quartzite, serpentine, and soapstone