Schorl-1A from Langesundsfjord (Norway)

A crystal fragment of schorl from Langesundsfjord (Norway), showing a zonation with a biaxial optic behavior in the rim, was studied by electron microprobe analysis, single-crystal X-ray diffraction, Mössbauer, infrared and optical absorption spectroscopy and optical measurements. Measured 2 V x is 15.6°. We concluded that biaxial character of the sample is not due to internal stress because it cannot be removed by heating and cooling. Diffraction data were refined with a standard R 3 m space group model, with a = 16.0013(2) Å, c = 7.2263(1) Å, and with a non-conventional triclinic R 1 space-group model keeping the same hexagonal triple cell ( a = 16.0093(5) Å, b = 16.0042(5) Å, c = 7.2328(2) Å, α = 90.008(3)°, β = 89.856(3)°, γ = 119.90(9)°), yielded R all = 1.75% (3136 unique reflections) vs. R all = 2.