Volume 20, Number 5, January - March 1999

AUSTRALIAN CHINESE WRITING STONE

Alex Bevan BSc (Hons) PhD (Lond), Peter Downes BSc (Hons), Jenny Bevan BSC (Hons) Dip. Geochem. (Oxon)
Department of Earth and Planetary Sciences, Western Australian Museum

ABSTRACT
Plagioclase-porphyritic basaltic rocks within the Mount Roe Basalt (around 2760 million years old) occur in the Pilbara Region of Western Australia and have lapidary and decorative use. Popularly named Chinese writing stone or sometimes chook's foot rock, because of the appearance of the porphyritic crystal groups, the rocks are variably weathered and range from dark, fresh material to greenish-grey, highly altered material. Depending on alteration the rocks take a moderate to good polish. The uses of this attractive rock may include carving, and also other decorative purposes such as inlays. The rock resembles a similarly named porphyritic basalt from the USA.

GemScan II

T. Linton, R. Pemberton, A. Cummimg (Qld), B. Sweeney (Tas), N. Masson (Vic)
G.A.A. Instrument Evaluation Committee Report

ABSTRACT
Use of surface reflectance meters in gemmology dates from 1959. Continuing developments in design, combined with new electronic technology, have improved the stability of digital readouts possible with these instruments.

GemScan International market a Queensland designed and manufactured surface reflectance meter - the GemScan II TM. This instrument has been purpose-designed for the use by jewellers who have limited access to conventional gem testing equipment, and yet still desire to identify gemstones and discriminate these from synthetics and imitations of similar appearance.

Gemstones and other man-made materials, that have a refractive index or refractive indices greater than 1.81, are readily identified with reflectance meter type instruments. Presently no other relatively inexpensive simple-to-operate equipment is available to identify these materials.

The jewellery industry certainly would benefit from a reliable instrument, that would accurately identify gemstones, synthetics and imitations, both for the non-gemmologist jeweller and/or his or her customer.

MAKING AN APPRAISAL OF JADEITE

C.M. Ou Yang
Hong Kong Gems laboratory

ABSTRACT
Appraising jadeite is a complex process for which considerable hands-on experience is a prerequisite. One of Hong Kong's acknowledged experts presents her 4Cs, 2Ts, and 1V of jade appraisal.

A MISCELLANY OF ORGANICS: PART 2

Grahame Brown
ALLGEM Services, Albany Creek, Queensland

ABSTRACT
A further complication of interesting laboratory reports that emphasise the unique challenges often posed when gemmologists are required to identify unusual biological gem materials.

NEW OPAL CARVING FACTORY AT KHAO YAI, THAILAND

Robert R. Coenraads¹, Paul E. Elmer^2
1Frenchs Forest, NSW
²Khao Yai, Thailand

ABSTRACT
Descriptions of a unique Thai factory for processing Queensland boulder opal into items of jewellery and other decorative objects, its personnel, products and its modus operandi.

SAPPHIRES FROM JIZERSKÁ LOUKA, CZECH REPUBLIC

Petra Maliková
The Charles University, Prague, Czech Republic

ABSTRACT
In spite of being the most important deposit of alluvial sapphire in Europe, until this investigation the origin of sapphire from Jizerská Louka in North Bohemia, Czech Republic, had not been establsihed. Two hypotheses were advanced to explain the source of these sapphires: one proposed a granitoid pegatite origin, the other proposed origin in a basaltic vent breccia. This study has revealed that the optical features, inclusions, and surface patterens of Jizerská Louka sapphire are very similar to those found in and on sapphires from Thai and Australian alluvial deposits - thus suggesting a basaltic origin for Jizerská Louka sapphire.