Metamorphic rocks are rocks that have "morphed" into another kind of rock. These rocks were once igneous or sedimentary rocks. How do sedimentary and igneous rocks change? The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change. If you exam metamorphic rock samples closely, you'll discover how flattened some of the grains in the rock are. Metamorphic rocks have been changed over time by extreme pressure and heat. Metamorphic rocks can be formed by pressure deep under the Earth's surface, from the extreme heat caused by magma or by the intense collisions and friction of tectonic plates. Uplift and erosion help bring metamorphic rock to the Earth's surface. Examples of metamorphic rocks include anthracite, quartzite, marble, slate, granulite, gneiss and schist. Anthracite is a type of coal with a high carbon count, few impurities and with a high luster (meaning it looks shiny). Marble is a metamorphic rock that is formed from the sedimentary rock limestone. Quartzite is a metamorphic rock that is formed from the sedimentary rock sandstone. Slate is a metamorphic rock that is formed from the sedimentary rock mudstone. Granulite is a metamorphic rock that is formed from the igneous rock basalt.
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