Crystal structure and chemistry of lithium-bearing trioctahedral micas-3T
Crystal structure and chemistry of lithium-bearing trioctahedral micas-3T (in Special issue dedicated to the memory of Luciano Ungaretti, Maria Chiara Domeneghetti (prefacer))
European Journal of Mineralogy (April 2003) 15 (2): 349-355
Chemical analyses and crystal structure refinements are reported for lithian siderophyllite-3T crystals from granitic pegmatites of the anorogenic Pikes Peak batholith, Colorado. These micas fall on the siderophyllite-polylithionite join, closer to siderophyllite. Single-crystal XRD refinements in space group P3 (sub 1) 12 (with R 0.034-0.036) on three samples indicate an ordered cation distribution with M1 and M3 positions substantially larger than M2. The tetrahedral cation-oxygen atom mean distances are 1.614-1.638 and 1.663-1.678 Aa for T1 and T2 sites, respectively consistent with Al (super 3+) enrichment in T2. The tetrahedral rotation angle (alpha ) is generally small (3.1-4.6 degrees ) and decreases with siderophyllite content. As Fe increases, the T1 tetrahedron becomes flatter, whereas T2 tetrahedron distortion is unchanged.