beryl, emerald, synthetic beryl, emerald, inclusions, gems

Gübelin and Robert M. Shipley, Jr., examine the identification of synthetic emerald following its introduction into the American jewelry trade, including reports of synthetic stones mixed with natural emeralds. Their account draws on five specimens studied by Gübelin and ten examined at the Gemological Institute of America’s Los Angeles laboratory. It discusses the German product marketed by I.G. Farbenindustrie as “Igmerald,” while an editorial note states that the American laboratory’s specimens came from an agent claiming independent manufacture in the United States. Synthetic emerald resembles natural material in color, luster, chemical composition, and crystal form. Unlike the pear-shaped boules associated with synthetic corundum and spinel, it develops as groups of well-formed hexagonal crystals, sometimes large enough to yield fashioned stones exceeding one carat. Straight growth bands parallel to the basal plane may occur, but external appearance and crystal habit provide little assistance in identification. The authors instead advocate combining optical measurements with microscopic examination. Their synthetic specimens show lower refractive indices and birefringence than the natural emeralds tabulated for comparison; representative synthetic values are 1.562–1.564 for the ordinary ray and 1.559–1.561 for the extraordinary ray, giving birefringence of approximately 0.003. Recent synthetic material displays relatively weak dichroism, contrasting with earlier reports of strong dichroism and indicating changes accompanying manufacturing progress. Pronounced anomalous double refraction produces birefringent patches and interference colors, attributed to internal strain probably associated with rapid growth. Previously published Laue photographs are cited as additional evidence of strain. Igmerald also exhibits absorption bands at 594 and 606 nm beyond the chromium-related features discussed for emerald; the authors propose these as diagnostic of that product and tentatively associate them with increased chromium content. Specific gravity is generally lower in synthetic material, but overlapping values limit its usefulness alone. Microscopic inclusions receive particular emphasis as a practical means of distinction. The examined synthetics lack the solid crystalline particles within fluid cavities that the authors associate with natural emerald’s three-phase inclusions. Separate minute solid particles may nevertheless occur in swarms. The most characteristic internal features are delicate featherlike, wispy, or veil-shaped formations resembling cracked lacquer or cloisonné. At approximately 250× magnification, these resolve into numerous small liquid inclusions containing rounded gas bubbles, arranged in broad, slightly curved groups. Nearly parallel rodlike features, interpreted as probable gas-filled cavities, are especially conspicuous in older synthetic material. The authors conclude that the combined evidence of refractive properties, strain patterns, absorption features, and characteristic inclusions permits reliable separation of the synthetic emeralds examined from natural stones, despite their close visual resemblance.