“blocky” texture may be observed even at lowpower (10×) magnification with transmitted light,but it may be missed if only reflected light is usedto examine the specimen.Pre-existing fractures in corundum—as well asthose created during Be diffusion—and boehmitechannels are often sealed, or “healed,” by the sameprocess. The molten flux enters the fracture orchannel, and the surfaces of the fracture or channel dissolve into the flux, where the dissolvedmaterial is held in solution until the temperatureis reduced. On cooling, the alumina then crystallizes out of the flux onto the walls of the fractureor channel, sealing it while at the same time trapping residues such as gas bubbles, flux remains,and glass. This “flux-assisted healing” of fractureswas well documented in rubies even before the