Petrology is the branch of geology that studies rocks, their mineralogy, composition, texture, structure and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together because both make heavy use of chemistry, chemical methods, and phase diagrams. Sedimentary petrology is commonly taught together with stratigraphy because it deals with the processes that form sedimentary rock. Modern sedimentary petrology is making increasing use of chemistry.

शैलविज्ञान या शैलिकी (Petrology) शैलों का, अर्थात् जिन निश्चित इकाइयों से पृथ्वी न्यूनाधिक निर्मित है उनका, अध्ययन है।