Facts on White Granite Rocks

Type

• Granite is an igneous rock, as opposed to sedimentary or metamorphic. It is formed from eruptions of magma due to shifting of the earth's tectonic plates. The three types of rock formations created from magma eruptions are basaltic, andesitic and granitic.

Formation

• Granitic magma contains 60 to 70 percent silica and generally reaches temperatures up to 1,500 degrees fahrenheit. This magma sits in the earth's lower crust deep beneath mountain regions. The temperature of the magma is high enough to partially melt the rock but, with the high silica content of granitic magma, it stays very thick. Granite is formed if the magma is intrusive or cools beneath the earth's outer crust. If the granitic magma is extrusive or erupts from the earth's crust in the form of lava, it becomes rhyolite.

Composition

• White granite is primarily comprised of quartz, alkali feldspar and biotite mica. Rocks are not classified as granite if they do not contain at least 20 percent quartz. They are also not classified as granite if more than 20 percent of the rock is made up of ferromagnesian minerals. Muscovite, biotite, amphibole and pyroxene are some minor essential minerals that can be present in granite.

Determination of Color

• Alkali feldspar, also referred to as potassium K-feldspar, is what determines the color of the granite. There are many different colors of K-feldspar. It can be pink, orange, red, green, white or any number of different shades and combinations of colors. White granite contains white K-feldspar. It is commonly marbled to varying degrees with biotite mica. The amount of marbling is determined by how the granite cooled when it was originally formed and the percentage of biotite mica. The greater percentage of biotite mica, the greater percentage of black marbling.

Location

• There are white granite deposits all over the world. White granite quarries are located in the United States in California, Georgia, Minnesota, New Hampshire, North Carolina and Vermont. White granite quarries are in Australia, China and India. Granite deposits are generally found when the granite is exposed through erosion of the upper layers of earth.