Differentiating veatchite polytypes using X-ray powder diffraction

摘要

Veatchite polytypes were properly identified from several localities relying solely on micro powder diffraction data. Diagnostic differences in their respective calculated patterns gave reliable identification results when compared with measured data. This permitted the confirmation of co-existing veatchite-1A and -2M on the same specimen from the Billie Mine, Inyo County, California as flat elongated crystals (-1A) and flat rhombic plates (-2M), respectively. On the specimen from the Sterling Borax Mine (Lang), type-locality for veatchite-2M, the polytype veatchite-1A was confirmed from radiating rhombic plates. From the type specimen for veatchite-1A (rhombic plates), collected from the borate deposit in Emet, Turkey, an additional unknown polytype of this mineral was discovered, but lacks suitable material for a complete characterization. At the Penobsquis deposit near Sussex in New Brunswick, Canada, only veatchite-2M was encountered. The area between 20 and 25°2θ holds the following diffraction signatures: -1A (two sets of double peaks at approximately 21.5 and 24.5°20), -1M (single peaks at 20 and 23°2θ) and -2M (double peaks at 20 and 23°2θ). The unknown polytype from Emet, Turkey differs from polytype-1A in that same range by having single peaks at the 21.5 and 24.5° instead of double peaks.