Metamorphic Rocks

The next biggest classification of rocks is somewhat similar to the sedimentary classification but the biggest difference is that metamorphic rocks were never deposited nor have they been broken down by causes of erosion. The classification of metamorphic rocks encompasses rocks that were igneous or sedimentary to begin with and were abruptly changed when they were subjected to a great amount of pressure as well as temperatures. There are two main types of metamorphism in rocks. 

Contact metamorphism takes place when a certain area is invaded by a big quantity of magma. When the magma starts to cool down it creates a zone from which geologically it is known as baked. This happens at the time the magma cools and it causes there to be a great amount of chemical changes and in many occasions re-crystallization in rocks that have been invaded or intruded. If the intruded rock consists of limestone, it would turn into marble. This baked area can extend for only a few inches or a few miles however it would depend on the conditions of when the magma first became intruded and when it started to cool down.

Kinetic or dynamic metamorphism is the other type of metamorphic rocks and this usually takes place when layers of rock are lifted up to form mountain ranges. Throughout this development big changes in the underlying rocks start to occur because of the changes in weight and the heat and pressure that occurs.

A few of the alterations in sedimentary rocks that take place include, shake to slate sandstone to quartzite, as well as bituminous coal to anthracite coal to graphite. Granitic igneous rocks turn into gneiss and the rocks that are more compacted turn out to be schist.