Structure and Growth Mechanism of Glauconite as Seen by High-Resolution Transmission Electron Microscopy

Marc Amouric and Claude Parron
Centre de Recherche sur les Mécanismes de la Croissance Cristalline CNRS—Campus de Luminy, Case 913, 13288 Marseille cedex 09, France
Laboratoire de Géologie Dynamique et Laboratoire associé au CNRS no. 132, Faculté des Sciences Saint-Jérôme, 13397 Marseille cedex 13, France

Abstract: The internal fabric of glauconite pellets has been studied by high-resolution transmission electron microscopy (HRTEM) for a better understanding of the glauconitization process. Typical “lamellae” which make up the glauconite pellets showed a spindle-like arrangement of layered crystallite packets. Three main mineral phases were detected: (1) well-ordered glauconite sensu stricto (d(001) = 10 Å) generally in the middle of the spindles; (2) a poorly ordered and undetermined layered-phase “X” with d(001) ∼ 12.5 Å, usually sandwiching glauconite such that the interface between the two materials is very sharp; and (3) a noncrystalline or gel-like phase located between the lamellae. A 14-Å smectite-like phase was rarely observed at the periphery of some grains. The glauconite crystallites clearly showed characteristic growth features (e.g., growth steps), whereas the unknown phase X exhibited destabilization characteristics. A structural analysis of the pure glauconite indicates that this dioctahedral mica was present in the IMd (disordered), 1M, and, to a much lesser extent, 2M1 polytypic forms. HRTEM revealed no interlayering of glauconite with the other layered phases. Rather, it appeared to have formed by a layer-growth mechanism at the expense of the unknown phase X which apparently converted into non-crystalline matter before converting to glauconite. The precursor function of the interlamellae “gel” phase during the evolutive process of glauconitization is not understood.

Key Words: Glauconite • Growth mechanism • High-resolution transmission electron microscopy • Mica • Polytype

Clays and Clay Minerals; December 1985 v. 33; no. 6; p. 473-482; DOI: 10.1346/CCMN.1985.0330601
© 1985, The Clay Minerals Society
Clay Minerals Society (www.clays.org)