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

Abstract

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, plagioclase and quartz. It occurs as massive aggregates of roughly equant grains. Basal parting is evident, and pyroxene cleavage is subtle. Indices of refraction are na 1.670(1), n3 1.675(1), and n1 1.695(1), and 2Vz is equal to 57.6(5)° at 589 nm. Pleochroism is nonexistent. Dcalc = 3.30 g/cm3. Cell dimensions determined from powder X-ray diffraction are a 9.730(4), b 8.873(3), c 5.275(2) Å, β 105.95(3)c. A single-crystal X-ray structural refinement was performed to determine bond lengths and angles. The empirical formula, based on results of electron-microprobe analyses and absorption spectroscopy indicating 0.30 wt.% H2O in the structure, is (Ca0.96Na0.04)(Mg0.86Al0.06 Fe2+0.05 diopside. Cathodoluminescence indicates that Mn2+ is present in the M1 site. Absorption spectroscopy demonstrates that Mn3+ does not contribute to the violet color.