(Follow this link for abstracts of past issues)

USE AND MISUSE OF OPTICAL MINERALOGY CONSTANTS IN GEMMOLOGY

Darko B. Sturman

Royal Ontario Museum, Toronto

ABSTRACT
Direct transfer of optical data, or concepts from mineralogy, to gemmology can cause confusion or misunderstandings. Two examples are given. First, the dispersion coefficient is not a reliable indicator of' ‘fire’ in faceted gemstones, and second, the rules for determination of birefringence can not be applied to 'doubling'. Factors contributing to doubling are described and diagrams are presented for fast and reliable estimates of the doubling effect in gemstones. Factors contributing to ‘fire’, and their relative importance, are not well understood at present. The only safe statement that can be made is that the dispersion coefficient is not a reliable indicator of dispersion of light into spectral colours as it enters the gemstone.

THE DIAMOND PIPELINE

Hsieh Hsien Lim
Perth, Western Australiao

ABSTRACT
The Diamond Pipeline is the term used to describe the distribution path of diamonds from the mine to the ultimate consumer, the general public. In this literature review the author first describes the individual components of the traditional diamond pipeline. Second, the author explains how this pipeline has and is being modified by changes that have occurred in the diamond industry since De Beers was privatised and revised its business strategy in response to perceived changes in the diamond market.

OPALS FROM JAVA

H. Sujatmiko¹, H. C. Einfalt², U. Henn¹

¹Bandung, Indonesia
²Bretten, Germany
³Idar Oberstein, Germany

ABSTRACT
Since the early 1970s, opal has been mined in the western part of Java from a strongly altered pumice layer within a Late Tertiary, volcanoclastic sequence. All together, about 100 small-scale miners are involved in the mining of opal from small underground workings. Mining occurs during, the dry season from May to September, with the miners working under contract conditions with the lease holder. The types of opal recovered range from common opal to hyalite, fire opal, and white and black precious opals that display a dominantly red, orange and green play-of-colour. Rough opal and partly preshaped and polished stones are sold at the mines by the lease holders, mainly to traders from Jakarta. The main market for finished products is in Indonesia, at trading centres in Jakarta, Bandung, Yogyakarta, and Bali. A small amount of Indonesian opal enters international markets.

KRÜSS REFRACTOMETER - ER 6010

T. Linton, R. Beatie, K. Hughes
Brisbane

ABSTRACT
A gemmologist's refractometer performs an essential function in gemstone identification. Unfortunately, refractometers imported from countries with high dollar exchange rates are now priced at levels that do not justify the extra expense associated with the purchase of such quality instruments. Gemmologists now have access to very high quality refractometers at half the price of expensive instruments. Krüss Optronics manufacture a range of such relativelv inexpensive, quality gemmological instruments one of which is the ER 6010 refractometer. This report evaluates the Features and performance of this refractometer.

A MISCELLANY OF ORGANICS - Part 3

Grahame Brown
Albany Creek, Queensland

ABSTRACT
A further compilation of interesting laboratory reports that emphasise the unique challenges often posed when the trade gemmologist is required to identify biological gem materials.

TRAPICHE OF MYANMAR

Kyaw Khaing Win
Yangon, Myanmar

ABSTRACT
Myanmar is the source of a range of trapiche gemstones that display a distinctive spoke-like star. In this paper the author illustrates a selection of these trapiche gemstones and hypothesises three possible origins for the unique appearance displayed by trapiche rubies and sapphires from Myanmar.