The study of rocks is called petrology. It is a branch of geology that normally studies the composition and distribution as well as the structure of rocks. Geology is a broad field that deals with the physical structure of the earth.
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The study of rocks is a branch of geology that is called petrology. There are three branches of petrology that are rightly named as the rocks they deal with; igneous, metamorphic, and sedimentary are the branches and rock types.