corundum, synthetic corundum.7, gems

Greek manufacturer A. Douros introduced a new flux synthetic ruby in early 1993. Grown by spontaneous nucleation in a lead-based solvent, the Douros synthetic ruby occurs as rhombohedral single crystals and twinned tabular crystals, as well as in clusters. The tabular crystals typically have intense red cores that gradually decrease in saturation to a near-colorless outermost layer; the rhombohedral crystals have a deep red body and a thin near-colorless layer on the rhombohedral faces, with umbrella-like growth patterns in some areas. Some samples contain distinctive inclusions of yellow residual flux with spherical bubbles. Chemically, the crystals are heavily zoned, and EDXRF analyses revealed variable trace amounts of Ti, Fe, Cr, and Ga, as well as some Pb; SEM-EDS identified the flux particles as lead-bearing. Microprobe analyses showed high Cr values in the crystal cores; in certain growth zones, Fe replaces Cr in the outermost layers. If inclusions or typical growth structures are not present, chemical composition appears to be the best means of separating these Douros synthetic rubies from natural rubies.