The crystal chemistry of alkali amphiboles from the Kajlidongri manganese mine, India.

The crystal structures of eight sodic-calcic and sodic amphiboles from the Kajlidongri manganese mine, India, have been refined to R values of 1-2% using single-crystal MoKa X-ray data. The crystals used in the collection of the intensity data were subsequently analyzed by electron- and ion-microprobe techniques. Site populations were assigned from the results of site-scattering refinement and stereochemical analysis, taking into account the unit formula determined for each crystal. These amphiboles range in composition from richterite to magnesioriebeckite to magnesio-arfvedsonite. All amphiboles contain Li, which ranges from 0.03 to 0.30 apfu and is completely ordered at the M(3) site. The amount of F in each crystal is equal to twice the amount of Li, suggesting that Li, which is ordered at the M(3) site, is locally associated with F at both the adjacent O(3) sites. The patterns of electron density in the A cavity and the populations at the A, O(3) and M(4) sites are in accord with previously proposed patterns of short-range order in monoclinic amphiboles. The compositions of these amphiboles lie along the join richterite-magnesioriebeckite and show a surprising degree of coherence in their major-element compositions considering the heterogeneity of the host rocks.