Schist

During metamorphism, rocks which were originally sedimentary, igneous or metamorphic are converted into schists and gneisses. If the composition of the rocks was originally similar, they may be very difficult to distinguish from one another if the metamorphism has been great. A quartz-porphyry, for example, and a fine grained feldspathic sandstone, may both be converted into a grey or pink mica-schist. Usually, however, it is possible to distinguish between sedimentary and igneous schists and gneisses. If, for example, the whole district occupied by these rocks has traces of bedding, clastic structure, or unconformability, then it may be a sign that the original rock was sedimentary.

Schist is a very durable rock, and because of that it has been used for centuries in construction. Buildings constructed from this rock can last for hundreds of years, and in addition to walls and flooring, it can be used in roofing and pillars. Schist is a common addition to many paints and is also used in jewelry.

Before the mid-18th century, the terms slate, shale and schist were not sharply differentiated by those involved with mining.