Slate is familiar to most people as a material which is used to roof houses in many parts of the world. It is a sedimentary shale-like rock that has undergone a low grade metamorphosis. During the process, it is highly compressed, and the mineral content within is flattened such that the resultant rock has very distinct cleavage planes. Slate is mostly made up of finely divided clay minerals, with the predominant ones typically being quartz, chlorine, and muscovite, although many others, such as feldspar, apatite, kaolin, and tourmaline can also be present. Some types of slate contain relatively large amounts of pyrite.