Choudhary G. (2011) Few remarkable stones tested at the Gem Testing Laboratory Jaipur, India. Presented at GIA International Gemmological Symposium 2011 held at Carlsbad, California on 29-30 May 2011. Abstract in proceedings volume.

Oriented needle-like inclusions were found in a flux-grown synthetic emerald. The needles appeared to be oriented along the prism faces; however, they intersected one another at approximately 60º. This synthetic emerald also contained numerous birefringent and elongated colourless crystals showing a hexagonal profile. A green quartz contained “lily pad”–like inclusions. The presence of colour zones/planes perpendicular to the optic axis indicated synthetic origin, which was confirmed by FTIR analysis. A dark bluish green serpentine was remarkable for its purple transmission in fiber-optic light. The exact cause of the purple transmission could not be determined, but it appeared to be the presence of minute particles arranged in planes. Other interesting materials included synthetic sapphire with natural-appearing milky zones, fluorite with corundum-like colour zones, and glass specimens with transparent crystals.

Choudhary G. & Fernandes S. (2011) Spectroscopic examination of commercially available quartz varieties- a gemmological perspective. Presented at GIA International Gemmological Symposium 2011 held at Carlsbad, California on 29-30 May 2011. Abstract in proceedings volume.

The lack of inclusions and visible growth features (colour zoning) makes the separation of colourless natural and synthetic quartz quite challenging. Though found colourless in nature, it can also be produced by heating other quartz varieties, such as amethyst, citrine, smoky, green (praseolite), and greenish yellow (lemon). Rock crystal, the purest variety of quartz, often contains aluminum (Al³⁺) impurities where the charge imbalance is compensated by a nearby interstitial alkali ion; this is a precursor for smoky quartz, which is produced by natural or artificial irradiation. Iron impurities, having different charge states, result in green (Fe²⁺), yellow (Fe³⁺), and violet (Fe⁴⁺). As a result, both natural and synthetic materials can be heated to 250-500ºC to produce the colourless variety. Infrared spectra offer the most valuable means for differentiating between natural and synthetic quartz, and for correlating the features observed in the spectroscopic data with colour varieties of natural and synthetic material. In our study, the OH, Al-OH/Li, Al-OH, Si-O / Al-OH, and Si-O related peaks at around 3593, 3480, 3379, 3305, and 3198 cm^-1 consistently appeared in natural rock crystal, while the 3584, 3421, 3297, and 3198 cm^-1 peaks were present in synthetic rock crystal; the most important peak in distinguishing natural from synthetic crystals was at 3480 cm^-1. The data also help differentiate between natural and synthetic versions of other coloured varieties and whether the colour is natural or produced by heating.

Choudhary G. (2011) Plastic coated quartz, imitating emerald, Gems & Gemology, Vol. 47, No. 1, pp 71-72

There are numerous natural, artificial, and treated materials that can imitate emerald quite convincingly. Recently, the Gem Testing Laboratory in Jaipur received for identification a green 73.58 ct drilled briolette. The owner of the stone was certain it was an emerald of Colombian origin. We concluded on the basis of gemmological and spectroscopic properties that this specimen was plastic-coated quartz. In the absence of gemmological testing, correct identification would have been problematic, especially for a trader or dealer equipped only with a loupe.

Choudhary G. (2010) A greenish yellow zoisite, The Australian Gemmologist, Vol. 24, No. 4, pp 90 - 91

This article describes the properties of an unusual greenish yellow zoisite that was submitted for identification to the Gem Testing Laboratory, Jaipur, India. Zoisite is best known as the violet-blue tanzanite, but this new colour variant provides another gemstone that can be used in jewellery. This specimen was also interesting for its striking strong trichroism. IR spectrum was also provided.