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Metamorphic Rocks Types • Form from pre-existing rocks (igneous, sedimentary, other metamorphic) • Chemically change under high heat, high pressure, and/or chemical reactions with heated fluids Hydrothermal Metamorphism • Super-heated fluids can change the composition of rocks in contact. • Areas near hydrothermal vents • Or from areas near active volcanoes Contact Metamorphism • Caused by extreme heat from magma • Magma intrusions Regional Metamorphism • Caused by extreme pressure over a large area (mountain building) Categorizing Metamorphic Rocks • Organized by texture and composition • First divided into foliated and non-foliated • Layers vs. Non-layered Categorizing Metamorphic Rocks • Foliated • Layers created during formation, crystals are squished parallel to each other. Can often be broken into layers • Examples – Schist (from shale) and Gneiss (from granite) Schist Gneiss Categorizing Metamorphic Rocks • Non-Foliated • Formed from blocky, interlocking crystals. • Does not break into layers • Examples: Quartzite (from sandstone) and Marble (from limestone) Quartzite Marble Categorizing Metamorphic Rocks • Additional Descriptions • foliated – gneissic- alternating bands of color – schistose-intermixed colors – Slaty-very fine smooth planes, easy to split, grey or green • non foliated – granoblastic-large rounded pieces – Hornfelsic- sharp angular pieces Rock Cycle • Forces that breakdown – Melting – Weathering: chemical (alters structure of a mineral) or mechanical (physical breakdown) – Erosion *Igneous rocks - more common on earth (most are below ground). *Sedimentary rocks are most common above ground Rock Cycle • Forces that form – Cooling – Deposition, Compaction, Cementation – Pressure Rocks • Continuous process with no set pathway