James Furman Kemp: A handbook of rocks for use without the microscope: with a glossary of the names of rocks and other lithological terms. 5. Aufl. , New York: D. Van Nostrand, 1918, pp. 180, 240: C. E. Dutton, 4th Annual Report U.S. Geological Survey, 1883, S. 95; Bulletin of the Geological Society of America, Volume 25 / Geological Society of America. 1914, p. 639
"4 Classification of rocks and description of physical properties of rock". Engineering Geology Field Manual(PDF). Vol. 1. US Bureau of Reclamation, Technical Service Center Engineering Geology Group. 1998. pp. 57–90. Archived from the original(PDF) on 17 June 2015. Retrieved 7 June 2010.
"4 Classification of rocks and description of physical properties of rock". Engineering Geology Field Manual(PDF). Vol. 1. US Bureau of Reclamation, Technical Service Center Engineering Geology Group. 1998. pp. 57–90. Archived from the original(PDF) on 17 June 2015. Retrieved 7 June 2010.