Pre-existing rocks subjected to high temperatures and pressures; they are change

Pre-existing rocks subjected to high temperatures and pressures; they are changed but not meltedHow are they formed? They are formed as a result of deep burial tectonic deformation (regional metamorphism) and/or contact with plutons (contact metamorphism)What are the two categories of metamorphic rocks? Foliated and non-foliatedWhat are the distinguishing characteristics between the two categories of rocks?Foliated rocks have a specific plane in which minerals have been preferentially rearranged due to the presence of clay and mica minerals. These include slate phyllite schist and gneiss. Non-foliated rocks do not have a specific planar orientation. They commonly have one mineral like marble (metamorphosed from limestone) or quartzite (metamorphosed from quartz sandstone).