Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light. Among the sedimentary rocks, chert and flint are cryptocrystalline. Carbonado, a form of diamond, is also cryptocrystalline. Volcanic rocks, especially of the felsic type such as felsites and rhyolites, may have a cryptocrystalline groundmass as distinguished from pure obsidian (felsic) or tachylyte (mafic), which are natural rock glasses. Onyx is also a cryptocrystalline. Agates such as the fairburn agate are also composed of cryptocrystalline silica.
- Dictionary of geological terms. Bates, Robert Latimer, 1912-, Jackson, Julia A., 1939-, American Geological Institute. (3rd Anchor books ed.). Garden City, N.Y.: Anchor Press/Doubleday. 1984. p. 120. ISBN 0385181000. OCLC 9412868.CS1 maint: others (link)
- Clark, Roger. (2009). South Dakota's State Gemstone : [autographed copy] ; Fairburn Agate. Clark, Mary, Jane. (1st ed.). Appleton, WI: Siverwind Agates. ISBN 9780966464023. OCLC 698895703.