Is petrology the study of all rocks, e.g aragonite, or just the study of sedimentary, igneous and metamorphic?

Question

Is petrology the study of all rocks, e.g aragonite, or just the study of sedimentary, igneous and metamorphic?

Answer 1

All rocks.  But if you know of any rocks which are neither sedimentary nor igneous nor metamorphic, the scientific community would like to know about it.

Answer 2

Aragonite is a mineral not a rock. Its a pseudomorph of calcite, so it has the same chemical formula CaCO3 but it has a different crystal structure.

If you were a specialist in studying aragonite or other minerals you would be a mineralogist.  If you were a specialist in studying rocks, then you would be a petrologist.