Biotite interlayer cations

Dyar M D (1990) Mossbaner spectra of biotite from metapelites. Am Mineral 75 656-666 Dymek RF (1983) Titaninm, aluminium and interlayer cation substitutions in biotite from high-grade gneisses, West Greenland. Am Mineral 68 880-899... 

FRONT COVER Perspective view of TOT layers in Biotite down [100] ([001] is vertical), produced by CrystalMaker, Red tetrahedra contain Si and Al, green and white octahedra contain Mg and Fe, respectively, and yellow spheres represents the K interlayer cations. Courtesy of Mickey Gunter, University of Idaho, Moscow. [Data S.R. Bohlen et al. (1980) Crystal chemistry of a metamorphic biotite and its significance in water barometry. Am Mineral 65 55-62]... 

The input structure for biotite was derived from the refinement reported by Hazen and Burnham (22). Potassium and magnesium were assumed to be the only cations occupying the interlayer and octahedral sites, respectively. Aluminum was assumed to occupy 1/4 of the tetrahedral sites. A layer spacing of exactly 1.0 nm was used to allow comparison to other 1.0-nm structures. 

Trioctahedral micas, such as phlogopite or biotite, are characterized by four distinct cation lattice sites tetrahedral (Z) sites occupied by silicon and aluminum octahedral (Y) sites, denoted Ml and M2, occupied by Al, Cr, Fe +, Ti, Fe +, Mg, and Mn and a large 12-fold coordinated interlayer X-site occupied by potassium, sodium, calcium, and other large cations. The low partition coefficients for lanthanides, uranium and thorium in phlogopite (<2X 10 ) indicate, however, that large highly charged cations cannot... 

---