Granite sample, close-up. Granite is an intrusive igneous rock consisting of the minerals quartz, feldspar and mica (black). This sample of granite is from an crystalline basement layer of rock in the Alps, a igneous rock layer that is found below sedimentary rocks. The rocks in these areas have cooled more slowly than other rocks, allowing large crystals to form, such as the one seen at centre. This sample is from Gotthard, Switzerland.