- GeoRef, Copyright 2008, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Two mechanisms operate within caves to produce concentrically laminated calcareous grains; the splash cup produces grains under agitated conditions so that abrasion and carbonate precipitation take place. The second, the rimstone dam and pool concretion occurrences, produces grains under nonagitated conditions. Agitated grains show distinct, compact laminations which display a pseudo-uniaxial cross caused by oriented crystal structure and commonly have a nucleus, smooth polished surfaces, a low insoluble residue content, and approach a spheroidal shape. Non-agitated grains have indistinct, porous laminations lacking oriented crystal structure. They commonly lack nuclei, have rough surfaces, are high in insoluble residues, and develop irregular shapes. The Bahamian grains show characteristics of agitated grains whereas the West Texas Permian reef pisolites are quiescent in character.