corundum, quality.10, Burma.12, gems

Describes sale of 15.97 ct ruby of Alan Caplan for $3,630,000 at auction in New York.

gems, spinel, Sri Lanka, sillimanite inclusions

A bluish-violet spinel from Sri Lanka with oriented inclusions was examined using microscopy, X-ray single-crystal diffraction, and electron microprobe analysis. The specimen displays four sets of lath-like, double-refracting crystal inclusions aligned parallel to the threefold axes of the host spinel. The inclusions are identified as one of the Al₂SiO₅ polymorphs, most likely sillimanite. The study also includes a general literature review on oriented inclusions and asterism in spinel.

corundum, synthetic corundum.7, gems

The West Coast laboratory recently received for identification the synthetic brown star sapphire ring illustrated in figure 14. Although synthetic star sapphires of this color are known (the GIA collection has some samples that were produced by Linde more than 20 years ago; similar material is also illustrated in K. Nassau’s Gems Made by Man, Chilton Book Co., Radnor, PA, 1980), this is the first one that we recall having received at this laboratory for identification. Although this stone is basically opaque, it has some semitranslucent areas near the surface. The stone has an R.I. of 1.76 (determined by the spot method), is inert to both long- and short-wave ultraviolet radiation, and shows no absorption lines or bands in the visible spectrum (400–700 nm). When the stone was viewed with the unaided eye, widely spaced curved color bands were visible, as well as the sharp star. These bands, which are medium brown and dark yellow-brown, could be followed around the top of the cabochon in a concentric pattern; they were only faintly visible on the base of the stone. With magnification, we observed tiny spherical gas bubbles just under the surface, as well as irregular veins and dark brown shallow cracks.

corundum, synthetic corundum.7, gems

In the Lab Notes section of the Summer 1987 issue of Gems & Gemology, we reported on unusually strong curved color banding in a synthetic yellow sapphire. More recently, the East Coast laboratory had the opportunity to examine two synthetic yellow sapphires that were unusual in other ways. When no color zoning or inclusions are present in a yellow sapphire, it is standard procedure to use immersion, magnification, and crossed polarizers to look for Plato lines as proof of synthesis. One of the two stones we examined displayed such strong Plato lines that they were actually visible without magnification or immersion (figure 15). In contrast, the second stone showed no discernible Plato lines at all, which is unusual for a flame-fusion synthetic yellow sapphire. This stone was proved to be synthetic when high magnification revealed the presence of several small gas bubbles. An interesting blue synthetic sapphire, also examined in New York, showed two sets of curved color banding that intersected each other at a very shallow angle. This is clearly indicated in figure 16 by the wedge of blue with its point almost dead center in the photo. The wedge marks the boundary between the two sets of banding, which are probably a result of changes in the growth conditions while the boule was being formed.

corundum, inclusions.5, gems

A 1.06-ct blue sapphire was submitted to the New York laboratory for identification. A spall cavity, the fire-skinned surface, and discoid fractures clearly indicated that the stone had been heat treated. However, the dark blue hexagonal color zoning seen through the table (figure 14) is unusual. It appears that a “phantom crystal” within the sapphire was affected by the heat treatment, leaving the edges fuzzy and partially diffused into the stone. When the stone was viewed with a Beck handheld spectroscope, the 450-nm (iron) line was quite strong. Perhaps this was originally a very dark sapphire that had been heated to lighten the color, with the perimeter of the “phantom crystal” remaining dark in spite of the treatment.

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.