“Cylindrite, medium gray, in dark gray massive sphalerite-wurtzite from Poopó, Bolivia. The cylindrite is cut perpendicular to the axis of elongation, showing how this hollow cylinder is formed from a single curved, sheetlike crystal. Filigree crystals in voids are either cylindrite or franckeite sheets. Daughter photo shows the same field with crossed polarizers. Plane polarized light (air). Field is 0.8 mm wide. Ben Schumer collection and photo. ”

“Cylindrite in massive sphalerite-wurtzite (brown internal reflections) from Poopó, Bolivia. Distinct anisotropic effects of the cylindrite emphasize the curved nature of the sheet forming the hollow cylinder. Note how the ends of the sheet are very tightly curled in on themselves. Very fine polishing scratches are also visible in the soft cylindrite. Crossed polarizers (air). Field is 0.8 mm wide. Ben Schumer collection and photo. ”