Metamorphic rocks

Metamorphic rocks compose the third large family of rocks. Metamorphic means «changed from». It shows that the original rock has been changed from its primary form to a new one. Being subjected to pressure, heat and chemically active fluids beneath the Earth’s surface, various rocks in the Earth’s crust undergo changes in texture, in mineral composition and structure are transformed into metamorphic rocks. This process is called metamorphism. As is known, metamorphic rocks developed from earlier igneous, sedimentary or metamorphic rocks by the action of heat and pressure.

Gneiss, mica schist, phyllite, marble, slate, quartzite belong to the same group of rocks. Having the same mineral composition as granite, gneiss consists chiefly of quartz, orthoclase and mica. However unlike granite, they have a schistose structure. It means that their constituents are distributed in bands or layers and run parallel to each other in one direction. If disturbed the rock cleaves easily into separate plates.