Choudhary G.(2008) An interesting opal, Gems & Gemology, Vol. 44, No. 2, pp 172- 174

We, at the Gem Testing Laboratory, Jaipur, India, examined an opal that exhibited an interesting and unusual growth pattern. The 14.04 ct oval cabochon had a semitransparent, colourless to milky white appearance with distinct play-of-colour. The specimen fluoresced a striking bright green to UV radiation, with a stronger reaction to short-wave than to long-wave UV.  With magnification and a fiber-optic light, the play-of-colour patches appeared to be restricted to zones or planes, which gave the impression of columns rising from a common base. Viewing along the column direction, we observed a cellular growth pattern. When the stone was examined immersed in water, the cellular growth structure showed unexpected whitish zones in a net-like pattern with pseudo-hexagonal boundaries, which is very similar to the “lizard skin” effect observed in synthetic or imitation opals. The overall features of this opal indicated natural origin, but FTIR spectroscopy was performed for confirmation

Choudhary G. & Golecha C. (2008) ‘Paraiba’ tourmaline and similar looking materials, Gems & Jewellery, Vol. 17, No. 1, pp 16 -18

The tourmalines from Paraíba, Brazil, display a distinctive bright electric blue-green colour that has led to their increasing popularity over the last two decades. The popularity of Paraíba tourmaline is now encouraging the jewellers, miners and manufacturers to provide a cheaper alternative. At the Gem Testing Laboratory of Jaipur we have encountered a number of gem materials which simulate the appearance of Paraíba tourmalines. Some of these include apatite, glass, cubic zirconia and synthetic beryl. Materials like apatite and glasses have been known as ‘Paraíba’ simulants for several years, but cubic zirconia and synthetic beryls have been launched recently on commercial scale. In view of the importance of and the demand for Paraíba tourmaline, we compiled details of simulants we have encountered and how they may be identified.

Choudhary G. (2008) Lead glass-filled colour-change sapphire, Gems & Gemology, Vol. 44, No. 1, pp 88 -89

Lead glass–filled rubies were first seen in the market in 2004. Much research has since been conducted to classify these rubies correctly, and the treatment is now well understood. However, such fillings are now being applied to sapphires as well. We encountered a 3.76 ct oval mixed cut sapphire with numerous eye-visible fissures. The stone appeared brownish green in daylight and fluorescent light and brownish purple in incandescent light. With magnification, the surface-reaching cracks showed an obvious blue-to-violet flash effect, which changed to greenish blue as the stone was moved. The fractures also contained large rounded and highly reflective flattened gas bubbles. In addition, white crystallites were observed in the filled cavities. These features are consistent with those reported in lead glass–filled rubies. Confirmation of lead was done using EDXRF

Choudhary G. (2008) An interesting synthetic sapphire, Gems & Gemology, Vol. 44, No. 1, pp 87-88

The sample was a 4.78 ct pear-shape mixed cut, with a brownish orange colour similar to that seen in beryllium-diffused sapphire. With magnification, surface-reaching, fingerprint-like inclusions were observed. They had a whitish appearance, suggesting they contained a foreign substance, as commonly seen in corundum exposed to high-temperature heating. A trail of dotted inclusions giving the impression of a broken (melted) needle was also visible. In addition, fine scattered pinpoints resembling gas bubbles were also observed. These features also indicated that the sapphire had been exposed to high-temperature heat treatment. Immersion in methylene iodide revealed a colourless girdle area, with most of the colour concentrated toward the center. As the stone was rotated and viewed from various directions, we observed wide colour zones that were separated by near-parallel curved boundaries, which are typical for flame-fusion synthetics. When the sample was viewed in the optic axis direction between crossed polarizers, strong Plato lines confirmed that it was a flame-fusion synthetic.