corundum, ruby, Vietnam.12, inclusions.5, gems

Grahame Brown examines the difficulties of distinguishing Vietnamese ruby from Myanmar ruby and identifying heat-treated Verneuil synthetics introduced into parcels represented as natural Vietnamese corundum. Discoveries at Luc Yen in 1987 and Quy Chau in 1990 supplied rubies and pink sapphires whose attractive colours closely resembled valuable Myanmar material. By late 1990, these stones were appearing in Australia through Vietnamese residents and dealers purchasing from Thai wholesalers. Brown reports that some parcels of rough and faceted ruby, as well as blue sapphire, contained convincing synthetic substitutes. Routine gemmological measurements provide little assistance because refractive indices, birefringence, specific gravity, pleochroism, fluorescence, and absorption spectra overlap among the materials concerned. Microscopic examination is therefore essential, although many inclusions previously considered characteristic of Myanmar ruby also occur in Vietnamese stones. Shared features include swirling growth structures, boehmite-decorated twin planes, rutile clouds, partly healed fractures, negative crystals, carbonates, apatite, mica, zircon, and pyrrhotite. Drawing on published research, Brown discusses potentially useful combinations of Vietnamese features, including blue growth-related zoning, rod-like pyrrhotite and carbonate inclusions, orange prismatic rutile, bluish clouds of fine rutile, and orange inclusions attributed to nordstrandite. These observations support cautious provenance assessment rather than simple separation by colour or one inclusion. The second problem arises because prolonged heating can diffuse the curved colour banding normally used to recognize flame-fusion corundum. Brown recommends examining every stone in immersion at 10–25× magnification, using diffuse transmitted light together with lateral fibre-optic illumination and rotating the specimen through different orientations. Residual diffuse banding, rounded or elongated gas bubbles, and partly fused whitish alumina near the original boule attachment can reveal synthetic origin. Other apparently reassuring features require caution: heating may generate natural-looking fractures in synthetic stones, and Verneuil corundum can display polysynthetic twinning. Conversely, elongated cavities in demonstrably natural Vietnamese ruby may resemble stretched synthetic gas bubbles. Photomicrographs document these overlapping appearances. Brown concludes that detecting synthetic additions and distinguishing Vietnamese from Myanmar origin require separate judgments, both founded on careful interpretation of multiple microscopic features. Chemical discrimination between natural sources in specimens lacking informative inclusions remained unproven at the time of the report.