[1] Univ British Columbia, Dept Earth & Ocean Sci, Vancouver, BC V6T 1Z4, Canada
[2] Nat Hist Museum Los Angeles Cty, Dept Mineral Sci, Los Angeles, CA 90007 USA
[3] Acad Sci Czech Republ, Inst Phys, Vvi, Prague 18221, Czech Republic
[4] Univ Gottingen, Dept Struct Chem, D-37077 Gottingen, Germany