Here's a breakdown:

* Geology is a broad field that encompasses the study of the Earth's physical structure, composition, processes, and history.

* Petrology is the specific branch of geology that focuses on the study of rocks, including their composition, texture, origin, and how they change over time.

* Mineralogy is the branch of geology that focuses on the study of minerals, including their chemical composition, crystal structure, physical properties, and formation.

So, while both rocks and minerals are studied in geology, you can get more specific with the terms petrology for rocks and mineralogy for minerals.