(Follow this link for abstracts of past issues)

Black opaque gem minerals

Seriwat Saminpanya, PhD, FGA, GG¹, Frederick Lin Sutherland, MSc, PhD, FAIG^2
1 Department of General Science, Srinakharinwirot University, Bangkok, Thailand.
external collaborator at University of Milano Bicocca, Italy
² School of Natural Sciences, University of Western Sydney, North Parramatta, NSW, Australia

ABSTRACT
Black opaque gem minerals (spinel, pyroxene and magnetite) occur in gravels associated with corundom in the alluvial deposits from Den Chai and Bo Phloi, Thailand. They were investigated for some, physical properties, chemical composition Raman characteristics and XRD patterns to clarify the misnomers being used in the gem markets and to distinguish individual black gem materials. The results indicate that the black spinel lies in the spinel-hercynite series, the black pyroxene is mostly augite and the magnetite lies in the magnetite-ulvöspinel series. The study also suggests that these minerals did not originate in the same environment as their mineral counterparts that are crystallised in basaltic rocks or as inclusions in corundum.

The thermal colour change of tanzanite

Grant Pearson
Mt Waverley, Victoria, Australia

ABSTRACT The thermally induced colour change of vanadium zoisite was spectrophotometrically measured, these data were analysed using a new data presentation enabling an analysis of the specimen's colour changes. The spectrophotometric results of the tanzanite colour-change are accompanied by illustrative photographs. The pleochroic colour differences of an unheated tanzanite crystal viewed from different directions were also demonstrated with the technique.

19.4 ct heat treated tanzanite described in the paper

Opal-C, Opal-CT & Opal-T from Acari, Peru

Prof. Franca Caucia¹, Dr Christian Ghisoli² ,  Dr Illaria Adamo², Dr Massimo Boiocchi^3
1 Department of Earth Science, University of Pavia, Pavia, Italy
² Department of Earth Science, University of Milan. Milan, Italy
³ Centro Grandi Strumenti, University of Pavia, Pavia, Italy

ABSTRACT
Descriptions of optical features, determined Specific Gravity, X-ray powder diffraction analyses and IR spectroscopic measurements have been applied to 25 translucent and opaque volcanic opals from the Peruvian mines of Acari region. X-ray diffraction patterns and IR spectra correspond to opal-C and opal-CT typologies, with also samples having a pure tridymitic composition (namely of opal-T type).

Opals showing different colours and transparencies can be classified into two classes, based on their lustre. The relationship between the lustre and the presence of phyllosilicate phases inside the opals has been assessed. The not previously observed Andean opals with vitreous-dull lustres (like porcelain) are both opal-C and opal-CT types that do not contain phyllosilicates.

Steller's Sea Cow bone
A rare carving material

Bobby Mann¹, Grahame Brown^2
1 Maryland USA
² Albany Creek, Queensland, Australia

ABSTRACT The rare biological gem material, bone from the now extinct Steller's sea cow from Bering Island, will be a challenge for gemmologists to identify. In this paper the authors will present a history of this marine marine mammal's discovery and extinction, the morphological and gemmological characteristics of its dense somewhat weathered bones, together with some practical suggestions how this bone can be discriminated from other bones commonly utilised for carving such as the long bones of bovines or camels, and the bony antlers of members of the deer family.

Selected opals from samples studied in this project. The upper samples are two opals-C with a vitreous-dull lustre, the middle samples are two opals-CT with greasy-waxy luster, the lower samples are opal-CT that do not contain phyllosilicates and exhibit a vitreous-dull lustre.

The Spoonmaker's diamond

Yrd. Doc. Dr. Murat Hatipoglu, Isil Meyanci, Cansu Turkdofan,
Deniz Comert, Ozge Temal
Dokuz Eylul University Izmir Vocational School

ABSTRACT
In this paper the authors review the history and various legends surrounding the acquisition of the historic Spoonmaker's diamond into the Ottoman Treasury. This 86 ct oval rose-cut diamond is presently on public display in the Turkish Republic's Istanbul Topkapi Palace Treasury Office.