Schist

Schist is a medium-grade metamorphic rock with medium to large grains of mica flakes in a preferred orientation (nearby mica flakes are roughly parallel).< Geological foliation (metamorphic arrangement in layers) with medium to large grained mica flakes in a preferred sheetlike orientation is called schistocity". It is defined by having more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar.^{[citation needed]} It has a preponderance of lamellar (flat, planar) minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. Schist is often garnetiferous. Schist forms at a higher temperature and has larger mica grains than phyllite.

The individual mineral grains in schist, drawn out into flaky scales by heat and pressure, can be seen by the naked eye. Schist is characteristically foliated, meaning the individual mineral grains split off easily into flakes or slabs. The word schist is derived from the Greek word σχίζειν schízein meaning "to split", which is a reference to the ease with which schists can be split along the plane in which the platy minerals lie.

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