Okay so all you need to do if find the process of rock you like and write it down but change what it says a little, here's some(A LOT!!) of info on metamorphic rocks
Metamorphism often occurs on two scales: contact and regional.
Contact metamorphism occurs relatively locally, in areas adjacent to
igneous intrusions or in areas that are in contact with hot water known
as hydrothermal fluids.
Typically this kind of metamorphism is caused by moderate
pressure and extreme heat that may last for a period of days to
thousands of years. In cases of contact metamorphism, the most extreme
metamorphism occurs at the contact point between the parent rock and the
intrusive magma or hydrothermal fluid. The degree of metamorphism then
decreases rapidly as distance from the heat source increases. Depending
on the source, zones of contact metamorphism may range from a few
millimeters to tens of meters.
In contrast to contact metamorphism, regional metamorphism occurs
over much larger areas. In areas such as rising mountain ranges, large
igneous intrusions can form and warp overlying strata increasing the
pressures above the intrusion. Also the extreme heat and pressures
caused by tectonic forces or deep burial will cause widespread
metamorphism.
and here's a link(you cant report me because i took a picture of the link, so ha-ha)
