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Rocks: Mineral Mixtures Chapter 4 Rock Definition Solid mixture of one or more minerals Rock Cycle Process in which one rock type changes into another rock type Three Rock types: Igneous Sedimentary Metamorphic Rock Cycle Mechanics: Sedimentary Weathering and Erosion – Forms clasts or grains Deposition Compacting and Cementing – Glues rock together, usually in layers Metamorphism Mechanics Metamorphism Rock undergoes Heat and Pressure Igneous Mechanics Melting Magma under crust Lava on Earth’s surface Cooling Solidification Rock Classification Color Composition Minerals determine make-up of the rock Texture Size and shape of grains – Fine – Medium – Coarse Igneous Rocks Rock formed from cooling magma or lava Three ways rock can melt: Increase in temperature Release of pressure Composition – Fluids and gases can lower melting point of rock Rocks will freeze between 700 and 1,250 Water freezes at 0 degrees Celsius Comes from Latin word for “fire” Composition Felsic Lightweight Light in color High silica Mafic Dark in color Dense or heavy Low silica Texture Intrusive Coarse grained Cools below crust Cools slowly Extrusive Fine grained Cools above the crust Cools quickly Composition and Texture Coarse-Grained Fine-Grained Felsic: High silica Granite Rhyolite Mafic: Low silica Gabbro Basalt Igneous Structures Volcanic necks Pluton and Batholith Lava flows and sills Sedimentary rocks Rock that is formed when sediments are compacted and cemented together Dissolved minerals in solution glue sediments together Forms at or near the Earth’s surface Sediment rocks form in layers known as strata Sedimentary Rocks Composition of Sedimentary rocks Classified by way it forms Classifications: Clastic Chemical Organic Clastic Sedimentary Made of fragments of other rocks Grain size helps identify rock Coarse = Conglomerate Medium = Sand/siltstone Fine = Shale Chemical Sedimentary Forms from solutions of minerals and water Precipitation dissolves minerals Rock forms through evaporation, or will crystallize out of water solution Organic Sedimentary Comprised of the remains of once living organisms Some limestone is formed this way Comprised of Calcium Carbonate Reacts with acid Sedimentary Rock Structure Stratification Layering of sedimentary rock Layers are called Strata Metamorphic Rocks Meta = Changed Morphos = Shape Rock that forms when composition and texture of preexisting rock is changed by heat and pressure Enlargement and rearrangement of grains Change occurs deep underground (plate tectonics) Two Common Types Regional Contact Metamorphism Types Contact Rock does not melt, but cooks into new rock Regional Enormous pressure Due to crust colliding Found near continental formations (mountains) Composition Conditions allow for minerals to combine making new rocks Some minerals will only form at certain pressure and heat ranges Texture Foliated Mineral grains aligned due to pressure Nonfoliated Lacks mineral alignment Commonly made of one or a few minerals
