Volume 20, Number 6, April - June 1999

GEOZOOLOGICAL PROSPECTING FOR GOLD AND GEMS

D.M .Colhester
West Pymble, N.S.W.

ABSTRACT
Geozoological prospecting employs the bioturbation activities of animals in the search for mineral deposits. It is the zoological equivalent of geobotanical prospecting where the occurrence and trace element chemistry of plants is used as an aid to locating mineral deposits.

Rabbits and ants have been used in South Australia to locate kimberlite occurrences. Zircon and sapphire grains have been seen on the surfaces of ant nest mounds located in gem gravels in northern New South Wales. In ancient times the burrowing activities of small animals have been used to locate and mine alluvial gold. The classical writers, Herodotus and Strabo, referred to these animals as 'ants' -- causing considerable confusion and debate for modern interpreters of their writings.

GEMMOLOGICAL MISCELLANY

Grahame Brown
ALLGEM Services, Brisbanem

ABSTRACT
An illustrated miscellany of short laboratory reports on a selection of man-made materials that include Chinese synthetic amethyst, French ‘opal’, unusual composite stones, faceted glass, synthetic moissanite, imitation rough sapphire, and blue-dyed lapis.

REFRACTOMETERS AND THE PIN-HOLE DISC (At close range)

T. Linton
Wellington Point, Queensland

ABSTRACT
High resolution images of the shadow edges on refractometer scales are possible from very small facets, provided a ‘pin-hole disc’ is inserted, at close range, between the eye and the eyepiece of the critical angle refractometer. Correct use of this technique allows refractive indices of the ordinary (w ) and extraordinary (e ) rays of uniaxial gemstones, as well as the maximum (g ), minimum (a ) and intermediate (b ) refractive indices of biaxial gemstones to be determined on these small facets.

WHITE CLIFFS: AUSTRALIA'S FIRST COMMERCIAL OPAL FIELD
A century of history

Gwen Rowe
White Cliffs History Group Inc.

ABSTRACT
White Cliffs, Australia's oldest commercial opal field, celebrates its centenary as an opal producer in late 1999. To celebrate this event two town blocks - that were once owned by the famous opal buyer E.E Murphy - will be converted into a tree-lined picnic area for the use of visitors to White Cliffs.

EVALUATION OF A TEACHING AID FOR 'VISUAL OPTICS'

T. Linton
Chairman, G.A.A. Instrument Evaluation Committee

ABSTRACT
Using the very inexpensive components of half a ping pong ball, an inexpensive handheld laser pointer, a glass microscope slide, and a small drop of colourless adhesive, American gemmologist Dr Don Hoover has created an effective lecture aid for demonstrating the major features of Alan Hodgkinson's Visual Optics to an audience of first time users of this method of gemstone identification without instruments. A preliminary word of caution, however, for this aid should be used with caution, for hand-held lasers do produce potentially dangerous radiation if allowed to make direct contact with eyes.

LH - an "OLD" Gemological Property

W. Wm. Hanneman, Ph.D.
Hanneman Gemological Instruments, Poulsbo, Washington

ABSTRACT
The critical angle refractometer, with its limited range, measures only the surface properties and not the bulk properties of a faceted gemstone, is of little use for identifying imitation, synthetic moissanite, or recently-marketed diffusion-coated topaz. These materials are better identified by instruments instruments such as the LustermetreÔ , Diamond EyeÔ , and Jeweler's EyeÔ that measure relative reflectivity (LH) on the Hannelnan luster scale.

PEARLS AND PEARL OYSTERS IN THE GULF OF CAHFORNIA, MEXICO
An Update

D. McLaurin MSc, E. Arizmendi MSc, S. Farell MSc, M. Nava M.Sc
ITESM-Perlas de Guaymas, Sonora, Mexico

ABSTRACT
In 1996, the first commercial marine pearl culture venture was started in the America continent. The farm is based near the coastal town of Guaymas, in the northern State of Sonora, Mexico. The farm utilises two Gulf of California native species of pearl oysters (Pteria sterna and Pinctada mazatlanica), both capable of producing dark and rainbow coloured pearls. Initially, only mabé pearls were produced, but production of whole pearls (rounds, baroque and including keshi) has increased. Problems that had not appeared before - during the experimental phase - made their appearance, resulting in increased oyster mortality. Fortunately these have been solved with simple solutions. The world markets have already received these "New World Pearls" with enthusiasm. This is due mostly to their unusual colouration.

GEMSTONES IN A NEW LIGHT

Alan Hodgkinson,
Scotland

ABSTRACT
The Nelson Pavilion Facet Fingerprinter, a simplified immersion technique utilising a plastic box, and several heating techniques now can be used as simple techniques for identifying synthetic moissanite and discriminating it from diamond and its imitations. These techniques are described and illustrated below.

BURMITE - BURMESE AMBER

U Tin Hlaing
Geology Department, Taunggyi University, Myanmar

ABSTRACT
For perhaps two thousand years Burmese amber (burmite), from the vicinity of Maingkwan in the Hukawang Valley of Myaranar's Kachin State, has been mined by the indigenous population of the area. Famed for its rich dark hues, and its toughness, this historic amber has long been prized by Chinese artisans. This paper reviews the occurrence, geology, gemmological properties, and patterns of inclusion in this little reported but long-used amber.