corundum, synthetic corundum.7, gems

This well-illustrated article examines (by SEM-EDX analysis) the inclusions in Russian hydrothermal ruby and sapphire manufactured by Tairus. Coatings on rough samples were found to be either boehmite or an unknown noncrystalline gel-like material. The following inclusions were observed in both rough and cut samples: solid inclusions of corroded copper (probably remnants of wire), isometric crystals and hexagonal platelets of copper, clouds and linear series of pinpoints of whitish reflective particles, tiny needles, and whitish particles (possibly alkali or calcium carbonates from the mineralizers). In pinkish red to red samples, the authors found fluid inclusion “fingerprints” or feathers, among which occur large three-phase (liquid-gas-mineral) inclusions associated with large tube-like negative crystals. The daughter minerals in the inclusions were identified (by crossed polarizers and heating/freezing [H/F] experiments) as carbonates. H/F experiments also revealed that the liquid phase is predominantly H₂O. By contrast, three-phase inclusions in natural rubies are often CO₂-rich with daughter minerals of diaspore, graphite, or mica. Of perhaps greatest interest to the practicing gemologist, the authors describe a simple gemological H/F test to distinguish between natural and synthetic hydrothermal rubies on the basis of three-phase inclusions. The copper inclusions also are indicative of synthetic origin.