Abstract
Microscopic examination of the natural faces of topaz have revealed micro-disk structure on (120) faces similar to those observed by Pandeya and Tolansky on dodecahedral faces of diamond. Similar disk-patterns have been produced in the laboratory on (001) cleavage faces of topaz by etching the cleavages in molten potassium hydroxide. The micro-topography of the disks studied by interferometry has revealed that they are slight elevations on the surface. Various experiments have been performed on matched cleavage faces of topaz and it has been established that the formation of the disks is due to the protective action of micro-bubbles formed on the surface during etching.