An Occurrence of Authigenic Nacrite

D. Bühmann
Department of Geology and Mineralogy, University of Natal Pietermaritzburg, Republic of South Africa

Abstract: Euhedral, pseudohexagonal nacrite was discovered as a thin layer coating a carbonaceous shale in the Sherwood Tunnel in Durban, Republic of South Africa. The nacrite apparently formed authigenically within a few weeks at ambient temperature by precipitation from pore solutions, probably as a result of evaporation. This observation suggests that nacrite can no longer be considered to indicate a high-temperature genetic environment. Precipitation from saturated pore solution may have been the mechanism of formation for this kaolin-mineral polymorph.

Key Words: Authigenesis • Kaolin-group mineral • Nacrite • Pore solution • Shale

Clays and Clay Minerals; April 1988 v. 36; no. 2; p. 137-140; DOI: 10.1346/CCMN.1988.0360206
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)