Hydroxyl Orientations and Interlayer Bonding in Amesite

R. F. Giese Jr.
Department of Geological Sciences, State University of New York 4240 Ridge Lea Road, Amherst, New York 14226

Abstract: The hydroxyl orientations in the 2H2 polytype of amesite, Mg2Al(SiAl)O5(OH)4, have been determine by minimizing the electrostatic potential energy as a function of OH orientation. The angles, ρ, between the hydroxyls and (001) vary between 81.5 and 88.8°. All surface hydroxyls form hydrogen bonds with oxygens of the adjacent layer. The OHs tend to tilt away from the higher charged AlVI ions, and the spread in ρ values is due to variations in the positions of the receptor oxygens. The inner hydroxyls noticeably weaken the interlayer bonding. The substitution of Al in both T and M sites creates a dipolar layer charge and the resulting attraction between layers forms an important part of the interlayer bonding. The 2H2 polytype of amesite has substantial interlayer bonding even with all surface hydroxyls replaced by fluorine. This is not true for a composition of Mg3Si2O5(OH)4 where a similar F for OH substitution destroys all interlayer bonding as in kaolinite.

Key Words: Amesite • Fluorine • Hydroxyl orientation • Interlayer bonding • Serpentine

Clays and Clay Minerals; April 1980 v. 28; no. 2; p. 81-86; DOI: 10.1346/CCMN.1980.0280201
© 1980, The Clay Minerals Society
Clay Minerals Society (www.clays.org)