Lithology

Lithology is the science of describing and classifying rocks based on their physical characteristics, including mineral composition, texture, color, and grain size. It emphasizes how rocks appear and behave in the field and in cores, rather than the processes that formed them. In stratigraphy and mapping, lithology is used to define lithostratigraphic units that are distinguished by rock type.

Field observations and hand specimen descriptions are the starting point, followed by microscopic petrography and laboratory analyses. Petrography under a microscope identifies minerals and textures; X-ray diffraction and geochemical assays can quantify composition. Lithology also encompasses lithofacies and engineering lithology, which relate to rock properties important for construction and groundwater flow.

Applications include petroleum geology, groundwater exploration, mining and mineral exploration, civil engineering, and environmental geology. Understanding lithology aids in interpreting depositional environments, reservoir quality, rock stability, and aquifer properties. In stratigraphy, lithostratigraphy studies rock units based on lithology rather than age.

Common lithologies include sandstone, shale, limestone, dolostone, and granite, as well as metamorphic rocks such as schist and gneiss. The term derives from the Greek lithos, rock.