Noun
The department of science which is concerned with the mineralogical and chemical composition of rocks, and with their classification: lithology.
A treatise on petrology.
Source: Webster's dictionaryPetrology Photomicrograph of a volcanic (basaltic) sand grain ; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter. Source: Internet