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ARGYLE TYPE 1A PINK DIAMONDS

Vanda Rolandi¹, Anna Brajkovic², Illaria Adamo³, Illaria Fontana^4
1 Italian College of Gemmologists (CIG),
external collaborator at University of Milano Bicocca, Italy
² Department of Geological Sciences and Geotechnologies,
University of the Studies of Milano Bicocca, Italy
³ Department of Earth Sciences 'Ardito Desio', University of the Studies of Milano, Italy,
⁴ Department of Science and Materials, University of the Studies of Milano Bicocca, Italy

ABSTRACT
Thirty-six (36) pink diamonds from the Argyle mine (Australia) have been examined, taking into consideration their surface characteristics, gemmological properties, and FTIR, UV-Vis and CL features. These specimens, resulting from the cutting of bigger diamonds, were rough, small and irregular in shape.

Hexagonal depressions, trigons, fractures and dislocation planes were the most common surface features observed. Anomalous birefringence, consisting of mosaic-like, cross-hatched or tatami patterns, were detected in all samples.

Absorption features in the IR revealed a low nitrogen concentration (< 100 ppm). All diamonds were type 1a and showed B-defect and/or more or less pronounced A-defect absorptions. Hydrogen was always present. A lack or absence of platelets was detected, allowing the conclusion to be drawn that any platelets had undergone a more or less catastrophic degradation.

The 415 mn (N3) peak, the 390 band, often superimposed on the N3 centre, and the 550 nm band, which possibly relates to dislocations and is responsible for the pink colour, may be considered the most important UV-Vis absorption features.

The CL imaging technique revealed distribution patterns created by lattice defects. A green emission band was tentatively ascribed to traces of natural radiation damage. CL spectra highlighted two wide components (respectively centred at 450 nm and 512-520 nm) that showed superimposed specific emission features, such as N3, H3 and H4 centres.

Taking into account the microscopic and spectroscopic features, it has been assumed that the examined pink diamonds developed in a strongly N-impoverished eclogitic environment, suffered post-growth plastic deformation, and experienced annealing, dissolution and resorption processes during mantle storage and eruptive emplacement

Key-words: Argyle, pink diamond, gemmological properties, surface features, spectroscopy, cathodoluminescence.

SPECTROPHOTOMETRIC TECHNIQUE FOR CHARACTERISING GEMSTONE COLOURS

G. Pearson
Mt Waverley, Victoria, Australia

ABSTRACT A spectrophotometric digital technique is proposed for characterisation of gemstone colours. The technique is considered to be especially applicable for monitoring and optimising colour-enhancement processes. it enables the description of a spectral 'colour distribution' quality of a material. More importantly, it enables detailed comparison between the colour components in the scans of different materials. This can be accomplished without the necessity of retaining comparison reference portions of materials for before-treatment and after-treatment visual evaluations. This is possible, even without subjective estimates being necessary to compensate for different depths of intensity of colour. The difficulties of metameric colour perception, in which the colours of materials with different absorption spectra can subjectively appear similar or even identical but only under certain particular qualities of illumination, are avoided.

Slices of untreated and treated heated olive-green Australian sapphire

DIAMOND: VARYING HARDNESS DIRECTIONS

Ric Cartier
Toronto, Canada

ABSTRACT
The hardness of diamond varies dramatically with direction, allowing diamond abrasive to be used to cut diamond. In 1961 J. Wilks & E. Wilks tested the depth of cut produced by grinding in various directions. This paper discusses the various hardness exhibited by each direction.

PHYSICAL FUNDAMENTALS BEHIND MODERN TECHNIQUES OF NATURAL DIAMOND ENHANCEMENT

Vins V.G.¹, Yelisseyev A.P.^2
1 New Diamonds of Siberia LTD, Novosibirsk, Russia, evins@acadent.org
² Institute of Geology and Mineralogy, Russian Acadamy of Sciences, Siberian Branch, Novosibirsk, Russia, elis@mail.nsk.rur

ABSTRACT
This extended abstract, although relatively technical in content, is authored by a world expert on enhancement of diamonds. The abstract does provide a full description of what happens when diamonds are subjected to irradiation-annealing, HPHT and other proprietary mixed techniques that are currently being used to value enhance diamonds. Persistence and dedicated reading will be rewarded with increased understanding. (Ed)

TOPAZ: PRISMATIC GROWTH LINES WITH ASSOCIATED LIQUID INCLUSIONS

Trevor Linton FGAA, Dip DT, Dip GR.
Linton Enterprises, Wellington Point, Queensland, Australia

ABSTRACT Crystals of Mount Surprise colourless topaz may contain growth handing parallel to prism faces. Liquid inclusions can be seen lying parallel to these growth bands. This occurrence raises the question: How can single and two-phase liquid inclusions form on growth bands at a growing face of a topaz crystal?

(110) Prisms with an inter-facial angle of 1240 on the front face of a topaz crystal

FROM A SINGAPOREAN GEM LABORATORY

Tay Thye Sun
Far East Gemological Laboratory, Singapore

ABSTRACT
Laboratory reports describing a carved yellow talc seal that was shown to be a composite imitation manufactured in China, and heat treated surface decorated chalcedony beads from Indonesia that superficially resemble Zi beads from Tibet and the Himalayan regions.

HANNEMAN-HODGKINSON GREEN STAINED JADEITE FILTER

Alan Hodgkinson
Portencross, Scotland

ABSTRACT
This paper describes use of a combination of the Hanneman-Hodgkinson Green Stained jadeite Filter and both long-and short wave Ultraviolet fluorescence to discriminate between natural coloured green jadeite (A-jade), acid treated-polymer filled jadeite (B-jade) , green stained jadeite (C-jade), acid treated green-stained polymer-filled jadeite (B+C-jade) and synthetic jade.

AGIL ILLUMINATION LOUPE

Trevor Linton
A report of the GAA Instrument Evaluation Committee