^Chesterman, Charles W. (1978). The Audubon Society field guide to North American rocks and minerals. New York: Alfred A. Knopf. p. 567. ISBN 0394502698.
^Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0-471-80580-7