Study of the Usambara Tourmalines (images and results coming)
Usambara tourmaline crystals. Photo: E. Skalwold	Photos courtesy of Asbjørn Halvorsen The images above show the view looking down the c-axis of a crystal fragment and a faceted stone. In the lower one, they are stacked together without changing the orientation.
Above I am actually doing this with different crystals and it is quite a dramatic effect to witness, but hard to hold the stones and direct the camera at the same time - will work on that shortly (see transmission curves ).
Sample Weight ct Shape Dimensions mm Hue Saturation Chelsea Filter Pleochroism Note FS 4.10 Faceted . . . . nε 1.629 nω 1.645 1a 14.62 Crystal Fragment . . . . . 1b 8.92 Crystal Fragment . . . . . 2a 6.41 Crystal Fragment . . . . . 2b 8.50 Crystal Fragment . . . . . Based on electron microprobe analysis, sample FS Cr2O3 percent by weight: 0.19; V2O5 and FeO are below detectable limits. FTIR Results:
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