Robert Folk

Robert L. Folk was an American sedimentologist and petrologist who taught at the University of Texas at Austin. He was one of the most influential figures in 20th-century sedimentary petrology.

Folk developed the standard classification systems for both carbonate and siliciclastic sedimentary rocks. His ternary diagrams and naming conventions are still taught in undergraduate geology courses worldwide.

His classifications gave geologists a precise, reproducible vocabulary to describe rock composition and texture based on grain types and proportions. The Folk carbonate classification, introduced in 1959, replaced vague descriptive terms with a rigorous framework.

Folk also contributed to studies of sedimentary textures, including his work on the nomenclature of clastic rocks and the statistical analysis of grain size. Later in his career he became interested in nanoscale structures in minerals.