Tobelite (Tob) crystal in the core of the quartz (Qz) vein from the SADC76 sample (A. in plane-polarized light and B. between crossed polars). Tobelite crystals with Chlorite (Chl) along the vein border from the SADC76 sample (C. in plane-polarized light and D. between crossed polars). E. Plot of M site vs. I site of tobelite grains, from the SADC76 sample, analyzed by electron microprobe. In addition to this, the average of tobelite analyses from Mesto et al. (2012) is plotted.