Volume 20, Number 12, October - December 2000

DISPERSION MEASUREMENT WITH THE GEMMOLOGIST’S REFRACTOMETER
Part 1

D. B. Hoover
Missouri, USA
T. Linton
Wellington Point, Queensland, Australia

ABSTRACT
In the past, the practicing gemmologist has had little interest in measuring the dispersion of gemstones. In part, this is because the property, dispersion, has little apparent use for the gemmologist. This lack of interest is evidenced by the scarcity of published papers discussing such measurements.

This paper reviews the history of the critical angle refractometer; which may be used to measure dispersion; the use of dispersion by gemmologists; and develops theory from which the critical angle refractometer may be calibrated to measure dispersion. Errors in prior published papers are explained. In Part 2, to follow, the practical aspects and problems of such measurements will be addressed.

NovaDiamond ^TM
COLOUR ENHANCED YELLOW AND YELLOW-GREEN DIAMONDS

Amanda S. Barnard
Melbourne, Victoria

ABSTRACT
Presented is a summary of properties and a discussion of mechanism of treatment of the NovaDiamond^TM colour enhanced yellow and yellow-green diamonds. Also included is an independent spectral examination of a specimen supplied courtesy of Novatek. It is intended that this paper should provide the reader with information necessary to assist in the effective identification of NovaDiamonds^TM, and other treated yellow-green diamonds.

RARE AUSTRALIAN GEMSTONES
MOONSTONE
A rare Queensland gemstone

Hylda Bracewell
Brisbane, Queensland

ABSTRACT
While the feldspars are chemically and structurally diverse minerals that are mined extensively throughout the world, any colourless variety that displays a bluish schiller is commonly termed moonstone, and is comparatively rare. Queensland gemmologists, members of the jewellery trade, and fossickers, are fortunate to have a small, yet prolific deposit of one of these rare gem feldspars readily available to them at Moonstone Hill, north of Hughenden in North Queensland. This paper describes this deposit and provides the gemmological properties and features of the moonstone that can be fossicked from this deposit.

RUSSIAN COLOURLESS SYNTHETIC DIAMOND
Now available in the market

Joe C. C. Yuan
New York

ABSTRACT
Colourless to near colourless synthetic diamonds, manufactured in Russia in the 'split sphere' apparatus, are now available on the US market. These type lla diamonds have a cubo-octahedral habit. When cut and polished they yield diamonds with colours mostly in the G-K range. The diamonds have identifying metallic inclusions, are magnetic, display ultraviolet luminescence that differs from that of natural diamonds, and yield a cross-shaped pattern of strain birefringence. Members of the trade, who do not have access to De Beers’ DiamondView^TM will have to rely on the observed presence of metallic inclusions, magnetism, and these diamonds un-natural fluorescence and phosphorescence, for identifying these synthetic diamonds.

AUSTRALIA'S GEMSTONE RESOURCES & THEIR MARKETS

Grahame Brown
Editor of The Australian Gemmologist

ABSTRACT
In this review Australia’s major gemstone resources were specified. Australia’s commercial production of diamond, opal, cultured South Sea pearls, chrysoprase, sapphire, and nephrite were detailed. Additional detail was provided about man-made gem materials presently being produced in Australia, and the support services available to Australia’s gemstone and related jewellery manufacturing industries. This review was presented to the APEC Gems & Jewellery Trade Y Technology Seminar that was held in Beijing during May 2000.