Metamorphic rocks are most often found in mountainous regions though they can be seen wherever there are signs of geological upheaval in an area. This type of rock is formed by the transformation of another rock type, a change that is usually triggered by tremendous heat, pressure or other violent phenomena. The forces that cause metamorphic rocks to form are so great that they change not only the appearance but also the chemical composition of an existing rock.
Gems and precious stones are some examples of metamorphic rocks. These stones are found deep underground or inside mountains. Precious stones usually form from igneous rock that has been metamorphosed by the weight of the earth pressing down on it over time. These stones are relatively rare because the process of forming them takes so much time and because they can be difficult to find and access.
Metamorphic rocks are also often found near the sites of living or extinct volcanoes. The heat caused by magma venting from the volcano can trigger chemical reactions that cause rocks to undergo metamorphosis. These types of metamorphic rocks are found at much shallower depths because the heat from the magma serves as a replacement for the heat generated by intense pressure.
There are two main types of metamorphic rocks. the first are called foliated metamorphic rocks and have a layered appearance, such as slate and phyllite. Non-foliated metamorphic rocks include marble and quartzite. Marble doesn't have the foliated, banded or layered look because it forms through intense heat, not pressure.