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Types of Rocks 1) Igneous Rocks - all crystallize from a hot melt: magma - below sfc, lava - above sfc - ~80% of the Earth’s crust Types of Igneous Rocks (w.r.t. cooling) a) Intrusive - Plutonic - from magma, coarse-grained (ex: granite) b) Extrusive - Volcanic - from lava, fine-grained (ex: basalt) Intrusive Bodies a) Shallow (< 2 km) Volcanic Neck - solidified magma of conduits that once connected a volcanic vent to the Earth’s surface with a deep magma reservoir Small Plutons (body of plutonic rock of any size or shape, intrusive rock - i.e. have intruded into the host rock) i) Dikes - discordant - cut across layers ii) Sills - concordant - parallel to layers Laccolith - concordant - more or less circular in shape, up to 3 km across b) Deep Batholith - continuous mass of granitic rock covering an area > ~100 km2, formed by rising large blobs of magma which are less dense than surrounding rock Stock - similar to a batholith but covers an area < 100 km2 2) Sedimentary Rocks - form from sediment deposited on the Earth’s surface, either from weathering & erosion of pre-existing rocks or chemical precipitation from solution, including secretions from water organisms. ~ 5% of the Earth’s crust. Lithification - transformation of unconsolidated sediment into solid rock Types of Sedimentary Rocks a) Clastic - from mechanical weathering - grains are broken down by a physical process & are deposited, consist of debris from erosion of older rocks or soil. Examples: i) Coarse-grained: conglomerate - formed by cementation of rounded gravel breccia - formed by cementation of angular fragments ii) Medium-grained: sandstone - formed by cementation of sand iii) Fine-grained: shale - formed by cementation of silt & clay particles b) Chemical - from precipitation from an aqueous environment - either precipitated directly by inorganic processes or by the actions of organisms, - consist of material formed within the sedimentary environment; - limestone is the most abundant 3) Metamorphic Rocks - from igneous, sedimentary or other metamorphic rocks that recrystallize under high T & P destroying old mineral grains & rock textures while creating new mineral assemblages & distinctive metamorphic textures & structures. Agents of Metamorphism a) composition of parent rock b) temperature - principal factor, can cause recrystallization & a loss of volatile compounds (CO2, water vapor) c) pressure - can cause recrystallization d) fluids e) time Classifications of Metamorphic Rocks (based on texture) a) Foliated - characterized by the parallel orientation of their layered minerals & varying degree of banding (color layering) ex: slate - from shale, schist - from shale, gneiss - from granite b) Non-foliated - no layers ex: marble - from limestone, quartzite - from quartz