Analyses of Palygorskites and Associated Clays from the Jbel Rhassoul (Morocco): Chemical Characteristics and Origin of Formation

Azzedine Chahi, Joelle Duplay and Jacques Lucas
Centre de Géochimie de la Surface, Institut de Géologie, 1 rue Blessig, 67084 Strasbourg Cedex, France

Abstract: The “Formation Rouge” from the Jbel Rhassoul in Morocco is composed of detrital sediments which have a lacustrine origin. The clays contained in the less than 2 µm fraction of the sediments are detrital phengites and illites, illite/smectites or smectites, and palygorskite. Due to the presence of well preserved long fibers, the palygorskite could not have been transported. They are authigenic and must have formed directly by precipitation from solutions rich in Mg and Al. The detrital illites are impoverished in K and tetrahedral Al. The illite/smectites or smectites, on the contrary, are K-rich but have a low tetrahedral charge. They are also richer in Mg and Fe and have a different crystal size, composition, and crystallinity from the illites. They most probably formed by crystallization, similar to the palygorskites, directly from the solution. The Al could have been provided by the detrital illite, which may have been unstable in an alkaline environment and released K and Al to the solutions.

Key Words: AEM • Jbel Rhassoul • Neoformation • Palygorskite

Clays and Clay Minerals; August 1993 v. 41; no. 4; p. 401-411; DOI: 10.1346/CCMN.1993.0410401
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)