According to the National Park Service, "Pegmatite refers to igneous rock with very coarse texture and unusually large, intergrown crystals. It consists mostly of quartz, feldspar, and mica. As magma cools and solidifies, water becomes concentrated. This concentration makes the magma more fluid and easier to squeeze, like toothpaste out of the tube, into the surrounding rock. The crystals can be very large—up to 6 feet (2 m) in length." To read more about Black Canyon of the Gunnison's geology, click here.