Metamorphic Rocks

A metamorphic rock is the result of a transformation of a previous rock type, the protolith. The protolith is subjected to heat (over 150 degrees Celcius) and extreme pressure which causes physical and chemical changes. This process is called metamorphism. The protolith mahy have been sedimentary rock, igneous rock or another older metamorphic rock.

Metamorphic rocks are formed deep beneath the Earth's surface by great stresses from rocks above and high pressures and temperatures. Metamorphic rocks become exposed at the earth's surface following erosion and uplift.

Some examlples of metamorphic rocks:


Gneiss is a common metamorphic rock formed from either igneous or sedimentary rocks.

Augen gneiss is a coarse-grained gneiss and resuts from the metamorphism of granite.

Marble is formed from the metamorphism of limestone and is composed mostly of the mineral calcite. Marble is used in scuptures, as a building material and in many other applications.

Quartzite is a hard metamorphic rock derived from sandstone. Sandstone transforms into quartzite through heating and pressure usually related to tectonic compression.

Pure quartzite is usually white to grey but it often occurs in various shades of pink and red due to varying amounts of iron oxide.
 

Slate is a fine-graine, homogeneous, metamorphic rock derived from and original shale-type sedimentary rock.

Slate can be made into roofing slates (also called roofing shingles) since it can be split into thin sheets. In the 18th and 19th century schools, slate was used for blackboards or individual writing slates.
 

Links to websites about metamorphic rocks: