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How does petrology differ from mineralogy?

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Faux amphibolite — geology A rock formation called “faux amphibolite,” from the Nuvvuagittuq greenstone belt in northern Quebec, dated to 4.28 billion years ago.

Petrology and mineralogy are distinct but closely related disciplines within the field of geology. Their primary differences lie in their scope and focus:

Mineralogy is the study of minerals, which are the basic chemical constituents of rocks and ore deposits. It focuses on describing and classifying the geometric, chemical, and physical properties of individual mineral species, as well as their internal crystal structures.1
Petrology is the scientific study of rocks. It examines the composition, texture, structure, occurrence, and origin of igneous, metamorphic, and sedimentary rocks. While mineralogy focuses on the properties of the building blocks themselves, petrology investigates how these minerals aggregate to form rocks and the geologic processes that govern their formation.23

Because most rocks are composed of minerals, petrology relies heavily on the principles and methods of mineralogy. Both disciplines often address similar questions regarding the physical and chemical conditions—such as temperature and pressure—under which minerals and rock assemblages form.231