Possible Rocks

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Possible Rocks Igneous: Name Classification Description Usually blackish-brown, sometimes greenish. Papier-mache look.Contains less than 5% quartz. Very dark, often black. Often contains phenocrysts of feldspars, olivine, and other dark minerals Dark gray to blackish gray, mottled. Evenly speckled with dark and light minerals, salt-and-peppery look. Gray or light green, very coarse-grained. Crystals of feldspar (pink or red), mica (dark brown or black), and quartz (clear pink, white, or black).C
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  Possible Rocks Igneous:Name Classification DescriptionAndesite ExtrusiveUsually blackish-brown, sometimes greenish. Papier-mache look.Contains lessthan 5% quartz. Basalt ExtrusiveVery dark, often black. Often contains phenocrysts of feldspars, olivine, andother dark minerals Diorite IntrusiveDark gray to blackish gray, mottled. Evenly speckled with dark and lightminerals, salt-and-peppery look. Gabbro IntrusiveGray or light green, very coarse-grained. Granite IntrusiveCrystals of feldspar (pink or red), mica (dark brown or black), and quartz (clear  pink, white, or black).Coarse-grained. Obsidian ExtrusiveShiny black.Volcanic glass, has a conchoidal fracture (see explanation of cleavage and fracture below) Be careful Pegmatite IntrusiveSame composition as granite but has very large, usually light crystals. Pumice ExtrusiveVery light gray. Also volcanic glass, but very light and bubbly. Only rock thatfloats. Rhyolite ExtrusiveUsually light grayish-pink. Made of the same minerals as obsidian and pumice, but did not cool as quickly. Scoria ExtrusiveDark gray, red, or black. Composed of basalt that cooled very quickly withtrapped air, so it is bubbly-looking. Sedimentary:Name Classification DescriptionAnthracite Coal Organic93-98% pure carbon. Shiny, scaly black. Conchoidal fracture. Can be used like black chalk. Arkose ClasticFormed mostly from feldspar. Gray or pink. Coarse grained, lookslike sandstone with redder tint (mostly quartz). Bituminous Coal Organic50-65% carbon Black. Not very shiny. Well-jointed, splinters under  pressure. Hardness: 2. Breccia ClasticConglomerate of sharp, angular fragments. Often forms after rock slides. Conglomerate ClasticConglomerate of smooth, rounded fragments. Has the largest grainsizes. Often forms in riverbeds. Coquina *Conglomerate of limestone shell fossils that are poorly cemented. *Clastically formed organic fragments. Diatomite OrganicLight tan, cream, or white. Extremely lightweight, lighter even thanchalk. Called fossil flour because it easily falls apart into flour-like dust. Dolomite/Dolostone ClasticLight gray, yellowish, pinkish. Contains a mixture of limestone, butat least 50% dolomite (mineral). Often contains fossils. Lignite Coal OrganicCoal that retains fibrous, woody structure. Less than 50% carbon. Limestone ClasticComposed of the fossilized shells of marine organisms. Chalk:White, soft, porous. Crystalline: white, hard, crystalline.  Fossiliferous: fossil structures can still be seen in rock. Oolitic:formed from small, round organisms that can still be seenindividually. Travertine: Color-banded, crystalline, often fibrous or concretionary. Sandstone ClasticEven, medium-sized quartz grains. Color variable, often tan, pink,or red. Shale ClasticVery small, microscopic particles. Soft, and splits into plates. Brownor black. Metamorphic:NameParentDescriptionGrain Color and Foliation MetamorphismGneiss Can be formed of almost any other rock.Medium to coarse grained.White or gray, butfoliated with dark rock.Must be less than 50%foliated.High grademetamorphism Marble Calcite or limestoneFine to medium grained.White, can be patchedwith green, gray, brown,or red.The metamorphism of limestone or dolomite. Phyllite SlateVery fine grains, wavy bands.Light, silvery-gray tolead-gray. Silky sheen Schist Almost any rock.Garnet Schist: Containsfairly large garnet inclusions.Mica Schist: Very shiny because of diorite inclusions.Silvery-gray, banded,wavy. Must be more than50% foliated with dark rock. Quartzite Pure sedimentaryrocksFairly small particles.White to patchy gray.Can range from sugarygreen to gray to pink.The metamorphism of sandstone. Slate ShaleVery small particles.Dark gray, shinyLow gradeMetamorphism. Minerals: By definition, minerals must have a definite chemical and crystal structure. There are a huge variety of minerals, many of which are very common. In order to understand minerals, it is helpful to understand basicchemistry and the periodic table. I won't attempt to go over all of that here, just look it up in any chemistrybook. Each mineral can be classified by ten different characteristics: group, formula, color, streak, luster,crystal structure, cleavage, fracture, hardness, and specific gravity. Definitions Group Minerals are organized into groups based on their chemical makeup. Native elements arecomposed of a single, pure element; Sulfides contain sulfur, arsenic, tellurium, or selenium;Oxides and Hydroxides contain oxygen compounds; Halides contain sodium, chlorine, fluorine,iodine, or bromine; Carbonates and Borates contain the carbonate or borate groups; Sulfatescontain the sulfate group; Phosphates, Arsenates, and Vanadates contain one of those chemicalgroups, and the Silicates and Tectosilicates contain the element silicon.  Formula Each mineral has a definite chemical composition. For example, fluorite is CaF2?. Again, if youneed a review on chemical formulas, look in any chemistry textbook. Color Color is not a good way to identify a mineral!!! Some minerals can be any color under the sun.While color can sometimes be useful, don't rely on it! Streak Streak is the color you get when you rub a rock across an unglazed piece of porcelain. Streak ismuch more useful than color because a mineral always has the same streak. Luster A mineral's luster is the way it reflects light. Descriptions of luster are very subjective, butsometimes useful. Common types of luster are vitreous (glassy), adamantine (brilliant or gem-like), resinous (resin-like), greasy, pearly, waxy, and silky. Crystal Structure I can describe each type of crystal structure, but you should also get a good mineral book, like thePeterson Field Guide, and read the section on crystal structure. Isometric Three axes of symmetry, all at right angles to one another, and all of equal lengths. Tetragonal Three axes of symmetry, all at right angles to one another, two of the same length and oneshorter. Hexagonal (Trigonal) Four axes of symmetry; three are of equal length and lie in the same plane at 120 degrees,the other can be any length and lies at right angles to the others. Orthorhombic Three axes, all at right angles to one another, of three different lengths. Monoclinic Three unequal axes, two at right angles, and the other inclined. Triclinic -Three unequal axes, none of which are at right angles to any others. Cleavage When a mineral has the tendency to break along smooth, flat surfaces, it has cleavage. If thebreak is perfectly smooth and shiny, it is said to have perfect cleavage. Cleavage can also bedescribed as good, distinct, or poor. Fracture Fracture is described as the way a mineral breaks (not along a cleavage plane). It can be uneven,hackly (sharp, jagged surface like broken metal), splintery, or conchoidal (shell-like). Hardness The Mohs Hardness Scale, which is used my most mineral collectors, is based on the hardness of other minerals. It is on a scale of one to ten, ten being the hardest. To test two minerals againsteach other, try to scratch each mineral with the other in an inconspicuous place. If they bothscratch each other, they have the same hardness. If only one causes a scratch, it is the hardest.Or, you can use common objects to see if the scratch or can be scratched by a mineral.  Hardness Mineral or Common Object1 Talc 2 Gypsum 2.5 Fingernail 3 Calcite 3 Copper penny 4 Fluorite 5 Apatite 5.5 Knife blade 6 Feldspar  6 Window glass 7 Quartz 7 Steel file 8 Topaz 9 Corundum 10 Diamond Specific Gravity Specific gravity (SG) is a measure of how dense a mineral is. It compares the mass of one gram of the mineral to the mass of one gram of water. So, a mineral with a SG of 4.5 is 4.5 times as heavyas water. With practice, you can tell whether a mineral specimen is light (usually less that 3.5) or heavy (greater than 4). Specific gravity can be helpful in detecting metallic minerals (they areusually heavier), or in cases where a mineral is unusually heavy. For example, galena is a gray,metallic mineral with a high lead content, and it is noticeably heavy. It is especially useful in thecase of barite, a white mineral which is unusually heavy because it contains the heavy metalbarium, but does not look metallic at all. Full Mineral List:Name Hardness SG Streak Color Group Crystal Shape Talc12.58-2.83WhiteLight to gray,greenSilicatesMonoclinicGraphite1-22.1-2.3GrayGreyNETrigonal/ HexBauxite1-32.3-2.7WhiteYellow, brownHydroxidesN/ASulfur1.5-2.52-2.1WhiteYellowNEOrthorhombicHalite22.1-2.2WhiteNumerousHalidesCubicGypsum22.32WhiteLight mediumSulfatesMonoclinicKaolinite2-2.52.6-2.63WhiteLight, mediumSilicatesTriclinicUlexite2.51.96WhiteColorlessBoratesTriclinicGalena2.57.58Lead-grayLead graySulfidesCubicLepidolite2.5-32.8-3.3ColorlessPink, purple,med.SilicatesMonoclinicCopper2.5-38.9Copper-redCopper or greenNECubicSilver2.5-310.5Silver-whiteSilverNECubicGold2.5-319.3Golden-yellowYellowNECubicBiotite2.5-42.7-3.4ColorlessDarkSilicatesMonoclinic
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