corundum, synthetic corundum.7, gems

The gemological, spectroscopic, and chemical characteristics of newly marketed Chatham flux-grown synthetic pink sapphires are documented through examination of four faceted stones weighing 2.73–4.19 ct and microscopic study of an 884 ct crystal. The material is essentially a lighter-toned counterpart of Chatham synthetic ruby. The faceted specimens are transparent, evenly colored, and medium light to medium purplish pink with fairly high saturation; the large crystal has comparable hue and saturation but a darker tone. Refractive indices are 1.768 and 1.759, birefringence is 0.009, and specific gravity ranges from 3.99 to 4.00. Dichroic colors are purplish pink and orange-pink. All specimens appear strongly red through a Chelsea filter and show absorption lines consistent with natural and synthetic ruby and pink sapphire. Long-wave and short-wave ultraviolet radiation produce essentially equally strong orange-red fluorescence with a weakly to moderately chalky overtone, without phosphorescence. This response differs from Chatham synthetic ruby, which generally fluoresces more strongly under long-wave radiation. Flux inclusions near the crystal’s surface fluoresce green, while deeper inclusions appear yellow, probably through combination with the host’s red fluorescence. Microscopic examination reveals primary flux inclusions ranging from large, granular masses to rows of minute droplets along growth steps. In two faceted stones, apparent primary flux particles form delicate intersecting rows producing a grid-like pattern, previously undocumented by the authors in synthetic gem materials and resembling arrangements of negative crystals in some natural spinels. Secondary flux inclusions occur as partially healed fingerprints, predominantly with undulating forms. Metallic inclusions include individual platelets, clusters of small rods and platelets, and dendritic formations; one stone contains a phantom layer of triangular and hexagonal platelets. Energy-dispersive X-ray fluorescence detects chromium, trace iron, and platinum in addition to aluminum. Platinum is attributed to the growth crucible and supports identification of the metallic inclusions. Chromium concentrations range from 0.027 to 0.200 wt.% Cr₂O₃, without an obvious relationship to specimen color, even after considering size differences. Most properties resemble those of other Chatham flux-grown corundums, while the ultraviolet response and unusual grid-like inclusions are noteworthy distinctions. Inclusions provide diagnostic evidence for separating these synthetic pink sapphires from natural material.