English geologist whose microscopic studies of thin slices of rock earned him the title “father of microscopical petrography.”

Sorby's early investigations were concerned with agricultural chemistry, but his interests soon turned to geology. He published works dealing with the physical geography of geologic periods, rock denudation and deposition, and the formation of river terraces.

Convinced of the value of the microscope as a tool in all sciences, Sorby began to prepare thin sections of rocks (about 0.025 millimetre, or ¹/₁₀₀₀ inch thick) for microscopic study in 1849. His subsequent findings demonstrated the value of petrography, the descriptive branch of the study of rocks. In his memoir “On the Microscopical Structure of Crystals,” in the Quarterly Journal of the Geological Society of London (1858), he championed the use of microscopic techniques in geology.

In 1865 Sorby announced a new type of spectrum microscope for analyzing the light of organic pigments, especially minute bloodstains. His research on meteoric geology led to studies of iron and steel, and he concluded that steel is a crystallized igneous rock. His later studies included the origin of stratified rocks, weathering, and marine biology.