Gneiss

Metamorphic rock, commonly rich in quartz and feldspar with a banded and foliated texture comprising bands of light colored minerals that alternate with bands of dark colored minerals. It is composed of mica, quartz, and schist, with additional iron, magnesium and silicates. It is formed at temperatures above 550 degrees Centigrade. Gneiss is similar to granite in composition and may be classified as a type of granite, but it is produced by the alteration of igneous and sedimentary deposits, whereas granite is formed of igneous deposits.