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Entry Task What questions would you ask in order to figure out what type of rock this is? Which rock is intrusive? Metamorphic Rocks “ A changed life” Meta=change Morph=shape Extreme heat and pressure change the texture and mineral composition of existing rocks Metamorphism Metamorphism: a change Metamorphic rocks: changed rocks; A rock whose texture or composition (or both) has changed due to increased temperature, pressure, or interaction with hot fluids Protolith- what the rock was originally Metamorphism can result in: • Recrystallization of minerals. • Crystallization of new minerals from old ones. • Plastic deformation of the rock. Metamorphic Grade Metamorphic Grade is the degree to which a rock has changed from the protolith. Low grade = low temperature 200 degrees Celsius (mica formed) Intermediate grade = 300-800 degrees Celsius High grade = 800+ degrees Celsius Factors Controlling Metamorphism Temperature, Pressure, Hydrothermal Fluids Two types of pressure: Directed Pressure: unequal pressure; greater from a particular direction Confining Pressure: general pressure from all directions. Types of Metamorphism Regional Contact Tectonic Regional Metamorphism Change created by rocks being buried under new rocks. The old rocks are exposed to heat and intense pressure. If the rock melts, it is no longer a metamorphic rock, it is an igneous rock. Contact metamorphism When magma comes in contact with the surface, the rocks at the surface are changed and become a metamorphic rock. How do you think they were changed? Tectonic metamorphism Rocks at plate boundaries are changed due to the heat and pressure of the plates moving past each other. Foliation Coarse-grained minerals separate and line up in bands. Example: gneiss (nice) Metamorphic Rocks Metamorphic Rocks Sandstone ~ quartzite Limestone ~ marble Shale ~ slate ~ schist Calcite, quartz, & hematite ~ garnet schist Granite ~ gneiss Schist A regional, medium grade metamorphic rock. What does that definition tells us about its origin? Schist Protolith: Phyllite Is this a regional or contact metamorphic rock? Your evidence? Slate Protolith: shale Graphite Protolith: bituminous coal