A classification for limestones and dolomites proposed in 1962 by W. M. Leighton and C. Pendexter, now used infrequently. The classification defines carbonate rocks by the percentage of grains, micrite, cement, and voids present. Limestones with more than 50% grains are named as ‘limestones’, prefixed by the name of the main grain type (e.g. ‘skeletal limestone’, ‘pellet limestone’); limestones with 10–50% grains are termed ‘micritic limestones’, prefixed by the name of the dominant grain type (e.g. ‘skeletal micritic limestone’); limestones with less than 10% grains are termed micritic limestones; limestones built by organic frame-builders are termed ‘coralline limestones’ or ‘algal limestones’ according to the type of frame-builder. Leighton and Pendexter also define carbonates with variable amounts of dolomite, calcite, and impurities on a triangular classification.