corundum, gems

The East Coast laboratory recently examined a natural sapphire that had three shallow pits on the pavilion [figure 13). Although such pits are frequently a side effect of heat treat-ment, they usually occur on the gir-dle. The unusual symmetry of the pits in this stone also suggests a different explanation. We surmised that the previous owner wore the sapphire in a ring alongside and in contact with a ring containing three dian~onds,which caused the abra-sions on the softer sapphire.trated in figure 14. Although syn-thetic star sapphires of this color are known (the CIA collection has some san~pletshat were produced by Linde more than 20 years ago; similar ma-terial is also illustrated in I<. Nas-sau's Gems Made by Man, Chilton Book Co,, Radnor, PA, 19801, this is the first one that we recall having received at this laboratory for identi-fication, Although this stone is basically opaque, it has some semitranslucent areas near the surface. The stone has an R.I. of 1.76 (determined by the spot method), is inert to both long-and short-wave ultraviolet radiation, and shows no absorption lines or bands in the visible spectrum (400-700 nm]. When the stone was viewed with the unaided eye, widely spaced curved color bands were visi-ble, as well as the sharp star. These bands, which are medium brown and dark yellow-brown, could be fol-lowed iiround the top of the c;ibochon in a concentric pattern; they were only faintly visible on the base of the stone. With magnification, we 013-served tiny spherical gas bubbles just under the surface, as well as irregular veins and dark brown shallow cracks (figure 15).