Common rock types

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Common Rock Types Colby Geology Igneous Rocks Classification based on composition and texture COMPOSITION Principally the rock-forming minerals Olivine Pyroxenes Amphiboles Micas Feldspars Quartz Constitute 95% of minerals in ALL igneous rocks COMPOSITION You can determine basic igneous rock composition just by the COLOR of the rock DARK COLORED igneous rocks = MAFIC LIGHT COLORED igneous rocks = FELSIC GRAY COLORED igneous rocks = INTERMEDIATE Color allows an approximation of igneous rock composition Related to Bowen’s Reaction Series (red vs green) 1200°C Gabbro-Basalt 900°C Diorite-Andesite Granite-Rhyolite 600°C TEXTURE TEXTURE reflects cooling rate of magma or lava SLOW COOLING = LARGE Crystals RAPID COOLING = SMALL Crystals SLOW COOLING = PLUTONIC RAPID COOLING = VOLCANIC TEXTURE Types of Textures Phaneritic Large crystals > mm Slow cooling rate = Plutonic Granite, Light Felsic Diorite, Gray Intermediate Gabbro Dark Mafic TEXTURE Types of Textures Aphanitic Small crystals < mm Fast cooling rate = Volcanic Rhyolite, Felsite Light Felsic Andesite, Gray Intermediate Massive Basalt Scoria Dark Mafic Rhyolite Felsite Metamorphic Rocks Rocks are fundamentally changed by HEAT and/or PRESSURE May be derived from ANY pre-existing rock type CLASSIFICATION based on the presence or absence of FOLIATION FOLIATION is the parallel alignment of the tabular minerals (micas and clay minerals) and by varying degrees of banding Metamorphic Rocks Types of Foliation Slatey cleavage very fine-grained rocks Usually found in slate and phyllite Metamorphic Rocks Types of Foliation Schistosity platy minerals visible Usually found in schist Metamorphic Rocks Types of Foliation Gneissic banding minerals segregated into bands Usually found in gneiss Metamorphic Rocks Foliated Rocks SLATE PHYLLITE Have slatey cleavage Rock splits along parallel planes SCHIST Has schistosity GNEISS Has gneissic banding Metamorphic Rocks Nonfoliated Rocks NO structure is apparent in the rock Rock is typically MASSIVE (monomineralic) Metamorphic Rocks Nonfoliated Rocks MARBLE Is composed of calcite (CaCO3), soft H = Will react to dilute hydrochloric acid Metamorphic Rocks Nonfoliated Rocks QUARTZITE Metamorphosed quartz sandstone Hardness = Metamorphic Rocks Nonfoliated Rocks ANTHRACITE COAL Formed from organic material (plant debris) Contains no minerals Metamorphic Rocks Nonfoliated Rocks GREENSTONE Composed of metamorphosed mafic igneous rocks Identification/Classification of Metamorphic Rocks Key on page 82 in lab manual Chart on page 95 in lab manual [...]... composition: Mostly quartz >25% feldspar 1/3 silt, clay and rock fragments = QUARTZ SS = ARKOSE = GREYWACKE Coarse-grained Clastic Sedimentary Rocks Conglomerate Breccia Medium-grained Clastic Sedimentary Rocks Sandstones Arkose Greywacke Qtz Sandstone Fine-grained Clastic Sedimentary Rocks Shale Sedimentary Rocks Chemical Sedimentary Rocks CHEMICAL SEDIMENTARY ROCKS precipitated from sea water (evaporites) initially... igneous rocks except MONOMINERALIC texture is crystalline if visible microcrystalline if not OOLITIC LIMESTONE CHERT DOLOMITE Oolitic Limestone Chert Dolostone CHEMICAL SEDIMENTARY ROCKS ROCK SALT or HALITE composed of halite (NaCl) microcrystalline to crystalline precipitates from sea water forms economic deposits Sedimentary Rocks Organic Sedimentary Rocks ORGANIC or BIOCLASTIC SEDIMENTARY ROCKS can... Igneous Rocks Key on page 75-77 in lab manual Chart on page 91 in lab manual IGNEOUS ROCK CLASSIFICATION COMPOSITION PHANERITIC APHANITIC GLASSY Dunite Ultramafic (Very Dark) Peridotite Mafic (Dark) Gabbro Intermediate Diorite (Gray) Felsic (Light) Granite Basalt Scoria Andesite Rhyolite Felsite Obsidian Pumice Sedimentary Rocks Clastic Sedimentary Rocks COMPOSITION Derived from pre-existing rocks Five... SED ROCKS CHERT microcrystalline composed of skeletons, microscopic in size made of SiO2 hardness = 7 may exhibit conchoidal fracture NONCARBONATE ORGANIC SED ROCKS PEAT composed of compressed plant debris basic building block of coal used as a fuel source in some areas Identification/Classification of Sedimentary Rocks Key on page 79-80 in lab manual Chart on page 93 in lab manual Metamorphic Rocks Rocks... from pre-existing rocks Five main constituents: Quartz Feldspar Rock fragments Clay (and clay minerals) Calcite TEXTURE CLASTIC – fragments of rock debris Classified by analyzing grain-size Sediment Size (mm) Particle Name >256 Boulder 64-256 Cobble 4-64 Pebble 2-4 Granule 0.063-2 Sand Sandstone 0.004-0.063 Silt Siltstone
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