Violet-colored diopside from southern Baffin Island, Nunavut, Canada

Diopside with an unusual violet color from southern Baffin Island, Nunavut, Arctic Canada, is found in calc-silicate lenses, associated with marialite , pargasite, phlogopite, calcite, apatite, titanite, talc, chlorite, plagio clase and quartz. It occurs as massive aggregates of roughly equant grains. Basal parting is evident and pyroxene cleavage is subtle. Indices of refra ction are n(alpha) 1.670(1), n(beta) 1.675(1), and n(gamma) 1.695(1), and 2 V(Z) is equal to 57.6(5)degrees at 589 nm. Pleochroism is nonexistent. D-ca lc = 3.30 g/cm(3). Cell dimensions determined from powder X-ray diffraction are a 9.730(4), b8.873(3), c5.275(2)Angstrom, beta 105.95(3)degrees. A sin gle-crystal X-ray structural refinement was performed to determine bond len gths and angles. The empirical formula, based on results of electron-microp robe analyses and absorption spectroscopy indicating 0.30 wt.% H2O in the s tructure, is (Ca0.96Na0.04)(Mg0.86Al0.06 Fe0.052+Ti0.024+)(Si1.89Al0.11)O5. 93OH0.07 The unusual color is due to intervalence charge-transfer between F e2+ and Ti4+ at the M1 site, and is observed owing to the low overall conce ntration of Fe in the diopside. Cathodoluminescence indicates that Mn2+ is present in the M1 site. Absorption spectroscopy demonstrates that Mn3+ does not contribute to the violet color.