Kaolinite is a clay mineral, as are illite and smectite. Kaolinite is formed by the alteration of alumino-silicate minerals, primarily feldspars. Kaolinite has a layered-sheet structure (a bit like the mica minerals) and occurs in very small crystals. Most specimens are aggregates of countless small crystals of kaolinite. Kaolinite is used in a variety of industrial processes, from the manufacture of pencil lead to making the paper in magazine pages shiny.
Pronunciation: kay•OH•lin•ite (accent on capitalized syllable)
Color: commonly chalky white
Luster: earthy
Diaphaneity: opaque
Hardness: 2
Specific gravity: 2.6
Cleavage/fracture: 1 (but too small to see)
Other distinguishing properties: Kaolinite may be confused with the sedimentary rock chalk, but chalk is composed of microscopic calcite in the fossilized skeletons of plankton, etc. Consequently, chalk effervesces (fizzes) in dilute hydrochloric acid.
Klein, C., and Hurlbut, C.S., Jr., 1999, Manual of Mineralogy (after James D. Dana) [21st edition, revised]: New York, John Wiley & Sons, 682 p.
Los Angeles County Museum of Natural History, The Photo Atlas of Minerals: nhm.org/pam/
Return to the Minerals page.
