GRANITE


Granite:
Granite is an igneous rock that is composed of four minerals. These minerals are quartz, feldspar, mica, and usually hornblende. Granite forms as magma cools far under the earth's surface. Because it hardens deep underground it cools very slowly. This allows crystals of the four minerals to grow large enough to be easily seen by the naked eye.

Granite - 2:
A coarse-grained intrusive igneous rock with at least 65% silica. Quartz, plagioclase feldspar and potassium feldspar make up most of the rock and give it a fairly light color. Granite has more potassium feldspar than plagioclase feldspar. Usually with biotite, but also may have hornblende.

Granite - 3:
An Intrusive igneous rocks, granite is a felsic rock with dominant minerals -- orthoclase (a pink, potassium-rich variety of feldspar), quartz, and lesser amounts of mica (both silvery muscovite or black biotite), hornblende, and plagioclase (white to gray,sodium-rich varieties of feldspar). Note that the word "granite" is used fairly liberally. Many rocks called "granite" are technically something different. The word "granitoid" or "granitic" implies felsic to intermediate intrusive rocks of many varieties, including granite.

Granitic:
A general term for intrusive igneous rocks that look similar to granite but may range in composition from quartz-diorite to granite. All granitic rocks are light colored; feldspar and quartz are visible in hand specimen.

Granite as a Building Material:
Granite is an excellent material for building bridges and buildings because it can withstand thousands of pounds of pressure. It is also used for monuments because it weathers slowly. Engravings in the granite can be read for hundreds of years, making the rock more valuable. Granite is quarried in many places in the world including the United States.

The "Granite State":
The State of New Hampshire has the nickname "Granite State" because of the amount of granite in the mountains of that beautiful state.

The Canadian Shield:
The Canadian Shield of North America contains huge outcroppings (surface rocks) of granite.



-- Excerpts from:
Volcano World Website, July 2001, USGS/NPS Geology in the Parks Website, 2003

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