Petrology

branch of geology that studies the origin, composition, distribution and structure of rocks

Petrology is a type of geology. It is concerned with rocks, how they form, and how they are used. It is between mineralogy, which is concerned with the minerals, in rocks, and geology, which tries to put rocks into a larger context.

The black rocks are "pelite", a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone