Volume 20, Number 8, October - December 1999

THE VISIBLE ABSORPTION SPECTROSCOPY OF EMERALDS
FROM DIFFERENT DEPOSITS

Inessa I. Moroz¹, Michael L. Roth², Valery B. Deich²
1 Institute of Earth Sciences, The Hebrew University of Jerusalem, Israel
2 Division of Applied Physics, The Hebrew University of Jerusalem, Israel

ABSTRACT
Emeralds from eleven gem-mining regions and Biron^Ò synthetic crystals have been studied by optical absorption spectroscopy. The results suggest that depending on relative concentration of chromium and 'iron' colour centres, optical spectra of emeralds may be specific for samples from different sources or deposits. Relative intensities of the Cr³+ (600 nm) and Fe ²+6 (810 nm) absorption bands reflect the Cr:Fe concentration ratio in samples of emerald. The presence of certain iron chromophores in emeralds may be considered as a distinctive sign in the emeralds. The absorption spectra of many emeralds exhibit 'mixed types' of absorption patterns that are related both to an emerald component (Cr³+ and/or V³+) and an aquamarine cotnponent (Fe²+ and Fe²+/Fe³+).

BROTHERS CORUNDUM: SAPPHIRES IN SRI LANKA

M.M.M. Mahroof
Colombo, Sri Lanka

ABSTRACT
The blue variety of corundum, which is termed sapphire, was and is the flag-bearer of the gem trade in Sri Lanka. This gem has been well respected since ancient times. Sapphire was recognised as an auspicious and royal gem from the time of Devanampiya Tissa, who ruled Sri Lanka during the third century B.C. Even when political upheavals took place, sapphire retained its status and importance. During Sri Lanka's colonial period (1550-1948), when the country was ruled successively by the Portuguese, the Dutch, and the British, sapphire decisively penetrated the European gemstone market. However, as the trade in sapphires is determined by the world market, its sale over the centuries has been subject to many fluctuations. Yet another recent constraint on world sales of sapphire has been the comparatively recent entry of geuda onto the market. Traditionally, other coloured varieties of corundum, except red (ruby), have the name sapphire suffixed to their particular colour.

RUBY FROM TUNDURU-SONGEA, EAST AFRICA
Some basic observations

G. Hamid¹, S.M.B. Kelly², G. Brown²
1 Melbourne, Victoria
2 Brisbane, Queensland

ABSTRACT
River gravels in the Tunduru-Songea area of Southern Tanzania are the source of the quality rubies of 'hot' pink to purplish red hue that are presently being actively marketed in Bangkok. Most, but not all of these rubies appear to have been heat treated prior to sale. In this preliminary investigation the authors describe the gemmological properties and morphological features of inclusions commonly observed in these rubies.

A PERSONAL CRITIQUE
of
'Modeling the appearance of the round brilliant cut diamond:
Analysis of brilliance' Gems & Gemology. 34, 158-183.

Garry Holloway
Melbourne

ABSTRACT
In 1919 Marcel Tolkowsky published a treatise on the brilliance of rotund brilliant diamonds. He proposed a single set of proportions which became known as the 'Ideal Cut'. No subsequent studies have improved on Tolkowsky's crown and pavilion angle combinations. although many support larger table sizes.

In the Fall 1998 issue of Gems & Gemology, GIA researchers published a complex analysis of 20,000 proportion variations using computer generated 'virtual' diamonds. This study, which focused on brilliance as the main factor of diamond appearance, found that the relationship between brilliance and the three primary proportion parameters of crown angle, pavilion angle and table size was complex, and that there were a ntunbcr of combinations of proportions that did yield high WLR (Weighted Light Return) values. GIA researchers are continuing this study to include 'fire' and scintillation. It is the opinion of these researchers that any cut grading assessment devised in the absence of this broader picture is premature.

This critique presents a possible solution, discovered by the author a decade ago, that he believes is supported by data provided in the GLA study.

CHATOYANT TREMOLITE (NEPHRITE)

Geoffrey A Tombs AM, FGAA
Croydon, Victoria

ABSTRACT
A description of the gemmological properties of and characteristic inclusions in chatoyant Taiwanese nephrite that is known locally as Taiwan jade.

VERNEUIL SYNTHETIC CORUNDUMS WITH INDUCED 'FINGERPRINTS'

J. Free, I. Free, G. Brown, T. Linton
G.A.A. (Queensland Division), Brisbane

ABSTRACT
Flux-healed quench-crackled Verneuil synthetic ruby and sapphire, that closely resemble Burmese ruby and Sri Lankan sapphire, are being manufactured as a byproduct of the routine heat treatment of ruby and sapphire in Chanthaburi, Thailand. In this paper, the gemmological properties and identifying features of these very effective look-alikes are described and illustrated.

OUR PAST HISTORY
STATEMENT RESPECTING THE OPAL INDUSTRY AT WHITE CLIFFS

T.C. Wollaston, Esq.
Adelaide

ABSTRACT
Evidence from the 1901 report of the Royal Commission appointed by the New South Wales Legislative Assembly to inquire into the opal-mining industry of White Cliffs.