Granite
From BWCAWiki
- For the river, see Granite River. For the lake, see Granite Lake.
Granite is a type of rock common in the BWCAW and is characterized by its speckled, "salt and pepper" appearance.
Granites are usually a white or buff color and are medium to coarse grained, and can be pink to dark gray or even black, depending on their chemistry and mineralogy. Granite is nearly always massive, hard and tough.
The average density of granite is 2.75 g/cm3; with a range of 1.74 to 2.80.
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Composition
Granite primarily consists of orthoclase and plagioclase feldspars, quartz, hornblende, mica, biotite, muscovite and minor accessory minerals such as magnetite, garnet, zircon and apatite. Rarely, a pyroxene is present.
Granite is mostly composed of the elements oxygen, silicon, aluminum, sodium, potassium, calcium, and iron.
Occurrence
Granite has been intruded into the crust of the Earth during all geologic periods; much of it is of Precambrian age. Granite is widely distributed throughout the continental crust of the Earth and is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents.
Granites in the BWCAW include the Saganaga tonalite around Saganaga and Seagull lakes, and outcrops on Crooked Lake, among others.
Origin
Granite is an igneous rock and is formed from magma. Granite magma has many potential origins but it must intrude other rocks. Most granite intrusions are emplaced at depth within the crust, usually greater than 1.5 kilometres and up to 50 km depth within thick continental crust.
References
Parts of this article are originally from WikipediA, The Free Encyclopedia.
