Volume 23, Number 12, October-December 2009

   
  • Argyle type 1a brown diamonds gemmological properties, FTIR, UV-VIS, CL and ESR features
  • Differentiation of naturally coloured and artificially irradiated blue topaz specimens
  • Zultanite, or colour-change diaspore from the Milas (Mugla) region, Turkey and editors addendum
  • Ancient deposit of blue chalcedony in Turkey
  • Laser inscription on diamonds
  • Prevention of cracking in Ethiopian opal
  • Scarselli exhibit of naturally coloured diamonds at the American Museum of Natural history

This issue includes an index to The Australian Gemmologist 2006-2009 Volume 23 pp. 1-592

(Follow this link for abstracts of past issues)

ARGYLE TYPE 1a BROWN DIAMONDS GEMMOLOGICAL PROPERTIES,
FTIR, UV-ViS, CL AND ESR FEATURES

 Anna Brajkovic1, Vanda Rolandi2, Roberto Scotti3

1 Department of Geological Sciences and Geotechnologies,
University of the Studies of Milano Bicocca, Italy
2 Italian College of Gemmologists (CIG), external collaborator at
University of Milano Bicocca, Italy
 3 Department of Science of Materials, University of the
Studies of Milano Bicocca, Italy
ABSTRACT
 Thirty-five light brown rough diamonds from the Argyle mine (Australia) were examined, taking into consideration their surface and internal characteristics, their gemmological properties and Raman, FTIR, UV-Vis, CL, and ESR features. Hexagonal depressions and etch patterns were the most common surface features observed. internal characteristics identified included irregular cracks, dislocation planes, minerals of the eclogitic series and graphite. Anomalous birefringence due to strain effects was detected in all specimens. Absorption features in the mid infra-red (MIR) revealed a moderately low nitrogen concentration (about 700 ppm). All diamonds were found to be type 1aAB and showed dominant B>A composition. Hydrogen was always present. Near infra-red (NIR) absorption spectra showed weak features ascribed to the AC1 amber centre.

The most common UV-Vis absorption features were a weak to moderate N3 peak, a broad unidentified and non-assigned peak at 482 nm and a broad 550 nm band (between 500 and 600 nm). The cathodoluminescent (CL) imaging technique revealed a general bright green emission. CL spectra highlighted two broad components, centred at 450 and 512-520 nm, with superimposed specific emission features. The electron spin resonance (ESR) spectra evidenced a weak triplet signal due to a N defect consistent with the W7 centre, closely related to the amber centre, and a more intense signal attributed to dangling C-C sp3 hybridised bonds.

Taking into account the microscopic and spectroscopic features, it was considered that the examined brown diamonds developed in a moderately N-impoverished eclogitic environment. They experienced dissolution and resorption processes, suffered platelet degradation and post-growth plastic deformation.

Key-words: Argyle, brown diamonds, gemmological properties, surface features, spectroscopy, cathodoluminescence, electron spin resonance.

   Hexagonal depressions on a diamond surface
Hexagonal depressions on the surface of Argyle brown diamonds, transmitted light, 100x.

Diamond trigons
Point-bottomed (pyramidal) and deep flat-bottomed trigons on the surface of a brown diamond, transmitted light, 400x.

DIFFERENTIATION OF NATURALLY COLOURED AND
ARTIFICIALLY IRRADIATED BLUE TOPAZ SPECIMENS

Ying Song1,2, Xinqiang Yuan2

1Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
 2Gemmological Institute, China University of Geosciences, Wuhan 430074, China

ABSTRACT
 Blue topaz is presently one of the gem industry's most commercialized gemstones. Being quite rare in nature. most commercially available blue topazes have been generated during the past thirty years by laboratory treatment with gamma radiation, neutrons or electrons, or with combinations of them. The origin of the blue color in topaz is not well understood, and a method to nondestructively distinguish natural blue topaz from its irradiated counterpart has been widely sought. This investigation showed that natural blue and artificially irradiated blue topaz could be distinguished by their different cathodoluminescence responses.

Key-words: cathodoluminescence, topaz, blue, irradiated, fluorescence, spectra

ZULTANITE, OR COLOUR-CHANGE DIASPORE FROM THE MILAS (MUGLA) REGION,
TURKEY AND EDITORS ADDENDUM

 Murat Hatipoglu1, Murat Akgun2

1 Dokuz Eylul University, IMYO, Izmir Multidisciplinary Vocational School, Gemmology and Jewelery Program, Dokuz Eyul Gemmological Testing Laboratory,
TR-35160 Buca-Izmir, Turkey
2 Murat Akgun, Milenyum Mining Co., Milas Bauxite Establishment,
TR-48200 Milas-Mugla, Turkey

ABSTRACT
 Diaspore or basic aluminium oxide has been known as transparent macrocrystals from Mugla in Turkey for several decades. A naturally occurring colour-change variety of the material from the same source in the Milas-Mugla region of SW Turkey has also been described and has been named "zultanite" since about 2005. Zultanite gems are moderately durable, with clarities ranging from eye-clean to some inclusions under magnification. Zultanite displays an alexandrite-like colour change dependent upon the nature of the incident illumination, and chatoyant material has also been found which can show a fine cats-eye effect. Recovery utilises traditional mining methods including both underground and open-pit excavations.

Keywords: Zultanite, diaspore, Milas Mugla (Turkey), colour-change, chatoyancy.

 		  Colour change Zultanite
Colour change in loose polished Zultanites.

ANCIENT DEPOSIT OF BLUE CHALCEDONY IN TURKEY

Murat Hatipoglu1 and Steven Chamberlain2

1 Dokuz Eylul University, IMYO, Izmir Multidisciplinary Vocational School, Gemmology and Jewelery Program, Dokuz Eyul Gemmological Testing Laboratory,
TR-35160 Buca-Izmir, Turkey
2 New York State Museum, Centre for Mineralogy, Albany, New York 12230, USA

ABSTRACT
The Saricakaya deposit (Eskisehir) is the largest and richest deposit of blue chalcedony in Turkey. The reserves and the grade of the chalcedony gem rough remaining in the face of present mining operations are reviewed, since its extraction historically began in the Roman Period. Some of its cutting and polishing characteristics are also discussed.

Key-words: chalcedony, blue, Anatolian, Eskisehir (Turkey), Roman.

LASER INSCRIPTION ON DIAMONDS

Ronnie Bauer R.A., Macc., B.A. (media), Post Grad. Bus.Admin., F.G.A.A., Dip. D.T., Registered Valuer 155

ABSTRACT
 The inscription of a logo, security code or a grading certificate number on the girdle of a diamond has been recognised commercial identification practice for about eight years. There has been little published during that time about the process or of the possible consequences of inscribing the girdles of diamonds.

Key-words: Diamonds, laser, inscription, girdle, logo, Diascribe, Sarin

   Laser inscribed girdle
Laser inscription applied to a diamond girdle.

PREVENTION OF CRACKING IN ETHIOPIAN OPAL

S.V. Filin, A.I. Puzynin
Dubna, JINR, Russia

ABSTRACT
 Many examples of opals from Ethiopia have a very beautiful play of colors. However, these gems are often prone to cracking only with the course of time or just mild heating. This unfortunate effect is associated with an appreciable water content in the open pores of the material. Internal stresses arise upon any dehydration resulting in surface shrinkage and progressive crazing and cracking. These defects make many Ethiopian opals unsuitable for use in jewelry.

Previously, the authors developed technology that enables synthesis of opal with closed porosity and chemical composition and physical properties quite similar to natural opal, This article describes the use of some methods developed in this technology with the intention of sealing the porosity in the natural opal from Ethiopia. The treatment was shown to remove the 5-60% mass of water in the pores in Ethiopian opal and to then seal them by impregnation with a silica sol. These gems were then less susceptible to dehydration and cracking even upon considerable heating.

The authors believe that this technology could also be applied to other natural opals with open pores which could substantially increase the stability of much natural gem opal.

Key-words: Opal, Ethiopia, cracking, prevention, supercritical, 'water, autoclave, silica sol.

SCARSELLI EXHIBIT OF NATURALLY COLOURED DIAMONDS AT THE
AMERICAN MUSEUM OF NATURAL HISTORY