Choudhary G. (2006) Plate tectonics and the gemstone deposits, Midlands Focus, 8^th issue, pp 13 -21

Plate Tectonics is the mechanism, which causes rock bodies to form. Most gemstones are associated with rock bodies, especially igneous rocks including pegmatites, hydrothermal veins, batholiths, lacoliths, dykes and pipes, and metamorphic rocks. The plates are the bases on which the complete crust rests, and they float over the hot magma in the mantle. The cooling of the hot magma after it has seeped through the crust, forms igneous rock, material for the formation of all the rocks. The eruption of magma depends upon the movement of plates, known as Plate Tectonics. There are three basic types of movement or motions between plates: Convergence, Divergence and Transformation. There are also several processes associated with the plate movement: Folding, Thrusting, Thickening, Subduction, Thinning, Mid-ocean ridges and Rift Valleys.  All the mechanisms result in the formation of different rock bodies which host a variety of gemstones.

Revised in 2014

Choudhary G. (2005) An unusual emerald with conical growth features, Gems & Gemology, Vol. 41, No.3, pp 265 - 266

The author examined a 5.37 ct emerald which displayed strong colour zoning in parallel layers and some of them contained conical growth features that resembled those seen in hydrothermal synthetic emeralds. The stone was immersed in bromoform. The conical growth features were seen along almost all the boundaries between the colourless and green zones. However, the individual cones were not restricted to single plane, and they varied in size. None of the chevron-type growth features were observed in the stone. With fibre optic light, the emerald exhibited a sheen caused by iridescent, roughly hexagonal platelets that formed along the planes in the green zones near colourless boundaries. Overall inclusion pattern and infra red spectrum concluded the emerald as natural

Choudhary G. (2005) Yellow hydrothermal synthetic sapphires seen in India, Gems & Gemology, Vol. 41, No.2, pp 182

Since about mid 2004, the Gem Testing Laboratory in Jaipur, India, has encountered approximately 20 synthetic yellow sapphires grown by hydrothermal technique. Most of these synthetics exhibited some scattered flake-like inclusions. In many samples, these flake like inclusions were concentrated in single plane along one side of the seed plate. A weak chevron growth pattern was seen only in few samples. IR spectra showed strong OH related peaks in the 3600 - 3300 cm^-1 region.

Choudhary G. (2005) Tanzanite buyers beware!, Midlands Focus, 6^th issue, pp 12-13

Tanzanite buyers and dealers had better now be careful as a new imitation has arrived in the market, Synthetic Forsterite. A number of synthetic forsterite samples have been tested at the Gem Testing Laboratory. Gemmological properties however, can differentiate it from tanzanite