In Brief

Granite

Image courtesy of Daniel A. Vellone, Northeast Regional Geologist, USDA Natural Resources Conservation Service.

Granite is 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.