synthetic beryl, emerald, gems

Thirteen faceted Russian hydrothermal synthetic emeralds are characterized through chemical analysis, physical measurements, polarized absorption spectroscopy, infrared spectroscopy, and microscopic examination, with comparisons to natural emeralds and published Russian synthesis research. The specimens range from 0.35 to 2.34 ct and include commercial material and a sample obtained from the Novosibirsk research institute. Their unusual composition combines low magnesium and sodium contents with substantial chromium, iron, nickel, and copper. These transition elements raise refractive indices and specific gravity, partly offsetting the effects of low alkali contents and producing values within the natural emerald range. Ordinary refractive indices are 1.580–1.586, extraordinary indices 1.573–1.579, birefringence 0.006–0.007, and specific gravity 2.68–2.70 for specimens without seed remnants. All samples are inert to long-wave and short-wave ultraviolet radiation, consistent with iron quenching chromium fluorescence. Polarized spectra indicate that chromium and nickel dominate color and pleochroism, with subordinate contributions from iron and copper. Pleochroism ranges from greenish blue to blue parallel to the optic axis and yellow-green to greenish yellow perpendicular to it. This appearance resembles certain natural emeralds but arises from different absorption mechanisms; earlier interpretations invoking an aquamarine component are rejected for the examined material. Infrared spectra reveal both type-I and type-II channel water, demonstrating that their coexistence cannot establish natural origin. Type-II water is attributed principally to association with lithium because sodium concentrations are very low. Microscopy reveals colorless beryl seed remnants in six specimens and growth zoning inclined approximately 31° to the optic axis throughout the sample group. Step-like zoning, cobbled seed boundaries, and characteristic blocks of subparallel crystal subindividuals provide particularly valuable diagnostic features. Inclusions include opaque platelets considered more likely hematite than platinum, birefringent crystals associated with fluid-filled growth tubes, and feathers containing liquid, two-phase, and three-phase inclusions. Some stones contain little foreign material, making growth structures especially important. The observed features are related to growth on specially oriented beryl seeds in steel autoclaves without precious-metal liners. Published industrial conditions include temperatures of 550–620 °C and pressures near 1,000 bar; autoclave corrosion and deliberate additions are considered possible sources of incorporated metals. The study concludes that trace-element composition, polarized ultraviolet-visible spectra, and immersion microscopy together provide effective recognition criteria, despite overlap with natural emeralds in routine physical properties and infrared water spectra.