Volume 22, Number 12, October - December 2006
|
|
(Follow this link for abstracts of past issues)
GEM CORALS
x-rAY dIFFRACTION, SOLID STATE nmr, ELEMENTAL ANALYSIS
Rosangela Bocchio1, Siliva Bracco2, Anna Brajkovic3,
Angiolina Comotti2, Vanda Rolandi4
1Department of Earth Sciences Ardito Desio, University of Milano,
Italy
2Department of Materials Science, University of Milano-Biocca,
Italy
3Department of GeologicalSciences and Geotechnologies, University
of Milano-Biocca, Italy
4Italian College of Gemmologists, (CIG),
External collaborator at the University of Milano-Biocca, Italy
ABSTRACT
The crystallographic and chemical features of twenty-one (21) gem-quality
corals belonging to both the classes Hydrozoa and Anthozoa of the phylum
Cnidaria have been investigated by powder X-ray diffraction (XRD), 13C
Magic Angle Spinning (MAS) NMR and laser ablation inductively-coupled plasma
mass spectrometry (LA-ICP-MS). The carbonatic matrices of the skeletons of
these corals were found to be calcite (in seven samples) or aragonite (in 14
samples). The content of Ca is higher in aragonitic corals than in the
calcitic corals. The values of Sr/Ca and Mg/Ca ratios indicate that the
incorporation of strontium or of magnesium in the coral skeleton depends on
the host carbonate polymorph. These ratios generally have good correlation
with the variation of the cell volumes, so that Mg and Sr content can he
considered the best discriminating chemical feature between these corals.
The trace element (Li, B, Ti, V, Cr, Co, Ni, Zn, Rb, Y, Zr, Nb, Cs, Ba, Pb,
U) content displayed broad variations that often overlapped both in calcitic
and aragonitic corals.
Key-words: coral, calcite, aragonite, X-ray diffraction, NMR, LA-ICP-MS, Sr/Ca, Mg/Ca, trace elements.
MEASUREMENT OF REFRACTIVE INDICES
WITH THE GEMMETERTM
- A Critical Evaluation
Laure Cosnier ING, FEEG
Masay, France
ABSTRACT
This study was conducted to make an overall evaluation of the GemmeterTM,
a new infrared reflectivity refractometer for determining low to high
refractive index readings. It was shown that several parameters could
influence the values of refractive index displayed: quality of the surface
of the gem tested, operating temperature, and the gemstone's dispersion.
Battery charge did not influence results. It was concluded that provided
certain precautions were considered, and multiple readings were averaged,
the Gemmeter does deliver reliable indices of refraction. The innovative
computerized functions of this instrument that display birefringence and the
possible identity of the gemstone under test were of questionable validity.
The performance of the Gemmeter and the conventional refractometer were
compared, and, as a consequence, a variation in the calibration procedure
for the Gemmeter is suggested.
identifying japanese freshwater cultured pearls from lake kasumigaura
Dr D.E. Jacob, U. Wehrmeister, Dr T. Häger, Prof. Dr W. Hofmeister
Institute for Gemstone Research, Johannes Gutenberg University, Mainz,
Germany
|
ABSTRACT A new analytical technique, utilising laser ablated Inductive Coupled Plasma-Mass-Spectrometry. or ICPMS, has been used to demonstrate discriminatory differences between Kasumigaura bead nucleated cultured freshwater pearls and Chinese cultured freshwater pearls. It has been shown that Kasumigaura pearls have a significantly lower Ba/Sr and Ga/Sr ratio than Chinese pearls, which reveal substantially higher and more variable ratios of these elements. |
|
| The Kasumigaura mussel |
BRANDED DIAMONDS
- Their Advantages and Limitations
a literature review
Dr Anne Lynch, MB, BS, FGAA
|
ABSTRACT This paper focuses on principles behind the marketing process and the arguments for and against branding of diamonds in the new environment that now exists in the diamond industry. The uses of mass psychology, market research, and targeted marketing are described. Case studies of the marketing techniques used by De Beers before and after 2000, Argyle Diamonds, and BHP/Billiton with its Ekati mine and Canadia brand are presented. This review of the literature was prepared to satisfy part of the requirements for the award of the GAA's Diploma in Diamond Technology. |
|
| The inscription on the girdle of a 'Candia' brand diamond |
ANOTHER IMITATION ELEPHANT PEARL
Grahame Brown
Albany Creek, Queensland
ABSTRACT
Artefacts purchased in Angkor Wat, Cambodia, which were claimed to be either
“elephant pearls” or “bamboo pearls”, have been shown to be man-made objects
that were manufactured from dense mammalian cortical bone. The identifying
features of this biological gem material are presented in this paper.
