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What Crystals are Found in Granite?

Granite is a form of igneous rock. It is composed mainly of crystalline silicate minerals such as quartz, feldspar, and mica. Granite is formed by molten rock deep in the Earth that has moved up into rock near the surface. The magma cools slowly, which allowed the grains of silicate minerals time to grow. The rate at which the rock cools determines how large the crystals grow. The more slowly the magma cools the larger the crystals. According to the University of Oregon website Ask Geo Man, granite, which also cools slowly, has large grains of crystal material and is the most common type of rock found on the continental land masses.

Quartz
- Quartz
  
  Quartz is one of the most common minerals on Earth. It is formed of silicon and oxygen atoms linked into molecules with a crystalline lattice structure. The interior of the earth is extremely hot and all the rock gets melted into lava. As the lava comes near the surface it can break through the surrounding sedimentary rock and cool slowly, allowing the quartz crystals to grow and link with other minerals in the granite.
Feldspar
- Feldspar
  
  According to Windows 2 the Universe, a National Earth Science Teachers Association website, feldspar is the most common mineral in the Earth's crust. The flat- or prism-shaped crystals are cream, pink, white or gray colored. Like quartz, feldspar is formed by the cooling of molten rock. The reason feldspar is commonly found in surface rock is because it is the lightest of all the silicate minerals. This allows the feldspar to float on the surface of the magma and accumulate closer to the surface.
Mica
- Mica
  
  When magma intrudes through sedimentary rock and cools slowly, the heavier mineral elements crystallize and produce granite. If the intrusion is slow and the cooling takes place over a very long period of time, large grained granite called pegmatite can form. Pegmatite has very large mineral crystals, including sheets of mica. Mica consists of many sheets of silicon oxygen having a tetrahedral shape. According to NASA and the Universities Space Research Association, the sheets are arranged like the pages in a book and held together by the ionic charges in the potassium, magnesium or iron contained in the mica. The type of metal contained in the mica determines its coloration.

Rocks & Minerals