Rocks

Kevin Connolly

Rocks

Rocks are composed of minerals. They are classified by how they are formed. There are three types of rocks: Igneous, Metamorphic, and Sedimentary

Igneous, Sedimentary, and Metamorphic Rocks

Pegmatite

Pegmatite is an igneous rock. The crystals form at a slow rate in the early stages of a magma's crystallization. The crystal sizes are usually large. The texture is very coarse. It is also non vesicular. Pegmatite has a light color, low density, and a felsic composition. Pegmatite contains 20% potassium feldspar and 20% quartz.
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Shale

Shale is an inorganic sedimentary rock. The texture of this rock is clastic. The grain size is clay which less than 0.0004 cm. Its composition is mostly quartz, feldspar, and clay minerals. Shale is also compact and can split very easily.
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Gneiss

Gneiss is a metamorphic rock that has a banding texture. It usually has a medium to coarse grain size. Its composition contains Mica, Quartz, Feldspar, Amphibole, Garnet, and Pyroxene. Its type of metamorphism is regional which is when either heat or pressure increases. Gneiss is a high grade metamorphism which mineral types segregate into bands.
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Rock Cycle

The Rock cycle is a model showing how rocks and sediments change over time. It shows external processes which are examples of weathering and erosion. It also shows internal processes which occur within the earth. As a particle goes through the rock cycle from sedimentary to metamorphic, density increases due to an increase in pressure
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