What's in Our Current Issue

Volume 23, Number 11, July - September 2009
Grahame Brown Memorial Issue - Part Three

(also included as a separate special issue: Rare Ivories - Grahame Brown)
 Volume 23 Number 11   Rare Ivories
  • Working the seam - The Tanzanite mines of Merelani
  • Aquamarine - natural or synthetic?
  • The genetic approach for identification of varieties of crystalline and amorphous silica
  • Micro-magma chambers in natural rubies and sapphires
  • Precious opal from Java
  • Presidium GCG and C-Master gem calculators

(Follow this link for abstracts of past issues)

WELCOME TO PART 3 OF THE GRAHAME BROWN MEMORIAL ISSUES.
Included is a separate special issue on Rare Ivories.

WORKING THE BLUE SEAM - THE TANZANITE MINES OF MERELANI

Vincent pardieu, Richard W. Hughes, with Guillaume Soubiraa, Michael Rodgers, Warne and Monte Chitty and Phillipe Brunot

ABSTRACT
 A colourful account of a visit to the Tanzanite gem mines of Merelani.		   Tanzanite
Tanzanite is strongly pleochroic. Photo © Wimon Manorotkul/Pala International; specimen courtesy of William Larson.

AQUAMARINE - NATURAL OR SYNTHETIC?

by Alan Hodgkinson

ABSTRACT
 Unlike emerald, with its long history of synthetic counterparts, identification of natural aquamarine in the past has given the gemmologist little difficulty using the basic gemmological resources. The distinction between an aquamarine and a loose or mounted simulant was usually quite straightforward.

Key-words: Aquamarine, natural, synthetic, hydrothermal, inclusions, rain, maxixe.

 

  
(Top) Hexagonal aquamarine prism
(Bottom) Unusual pyramidal termination

THE GENETIC APPROACH FOR IDENTIFICATION OF VARIETIES OF CRYSTALLINE AND AMORPHOUS SILICA

1 Balistsky V.S.    2 Balitskaya O.V.

1 Institute of Experimental Mineralogy of RAS, Chernogolovka, Moscow District, Russia

2 Russian State Geological Prospecting University, Moscow, Russia

The development of correlations between different gemmological characteristics and specific synthesis conditions of natural and synthetic quartz varieties and precious opal leads to a testing and identification approach defined as "genetic gemmology". Recognition of specific features that are known to be exclusively characteristic of either natural or synthetic origins enable determinations of the provenance of the gem material.

Key-words: Silica, quartz, crystalline, amorphous, opal, gem, identification, testing.

MICRO MAGMA CHAMBERS IN NATURAL RUBIES AND SAPPHIRES
a PICTORIAL EXAMINATION OF THE BEHAVIOUR OF SOME SOLID MINERAL INCLUSIONS IN CORUNDUM AT EXTREMELY HIGH TEMPERATURES

By John Koivula

ABSTRACT
 The behaviour of fluid inclusions in natural corundum during heat treatment processes at elevated temperatures has been examined before and is relatively well known. (Koivula, 1986). From such studies and observations the condition of fluid inclusions has in fact become an extremely useful means of determining whether or not a particular ruby or sapphire was heat-treated in an attempt to alter its color and/or clarity.

Key-words: Corundum, sapphire, ruby, heat treatment, inclusions, flux, cracks, voids, magma.

 		 
Magma blister formed on ruby by pressure from melt-damaged inclusion

PRECIOUS OPAL FROM JAVA
GEMMOLOGICAL PROPERTIES AND NANO-STRUCTURES

1 Tay Thye Sun, 2 Puah Chun Mok, 2 Sunny Liew Paul, 3 Mahardi Paramita,
4 Charles E.S. Arps, 5 Wilawan Atichat, 6 Emmanuel Fritsch,
7 We Weng Kang, 7 Kumala Wijaya.

1 Far East Gemological Laboratory, Singapore
2 Technology Centre for Life Science, Singapore
3 Adams Gemological Laboratory of Indonesia
4 National Museum of Natural History, Leiden, The Netherlands
5 The Gems and Jewelry Institute of Thailand
6 Institute des Materiaux Jean Rouxel, Nantes, France
7 Opal Trader and collector, Indonesia

ABSTRACT
 Precious Javanese opal or kalimaya, as it is called by the locals, has been mined in Central Banten, West Java. Indonesia, since 1970. Early January 2006, the four authors. Tay Thye Sun, Mahardi Paramita, We Weng Kang and Kumala Wijaya visited visited eight opal mining pits near the Cilayang village, Curuk Bitung District, Lebak Countv (between 106° to 106° 50 East and 6° 50 to 7° 0' South). At Cilayang, one pit was in operation at the time.

Cilayang produces white, brown, dark brown and jelly opal. Black opal is mined in other nearby gem-pits near the villages of Cikelurahan. Cimclingpin,; and Ciguriman.

Key Words: Opal, volcanic, Indonesian, Java, Banten, hydrophane, kalimaya		  
Hydrophane opal after soaking in water.

PRESIDIUM GCG AND C-MASTER GEM CALCULATORS
A REPORT FROM THE INSTRUMENT EVALUATION COMMITTEE

1 Trevor Linton FGAA, Dip DT, Dip. GR.
 2 Callum Curtis FGAA, Dip. DT.

1 Sophie Court, Wellington Point, Queensland 4160

2 Charles Rufus P/L, Suite 39, Gallery Level, Brisbane Arcade,
Queen St Mall, Brisbane, Queensland

ABSTRACT
 Estimation of weight when a gemstone is mounted in jewellery has previously relied on various methods of calculating gemstone weight from three dimensions. These techniques have relied on measuring calipers, books of tables, correction formula and electronic digital calculators. Simplification of these activities may improve productivity.

The Instrument Evaluation Committee examined two instruments that enable the estimation of a gem's weight by using a computer connected to a measuring gauge. The computer calculates an estimated weight for that species and shape of gemstone. Books of tables and calculators are no longer required with these new instruments.

Key Words: Gemstone weight calculation, Gemmological Instruments, C-Master, Presidium GCG.