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(Follow this link for abstracts of past issues)
AMBER-LIKE FOSSIL RESIN FROM NORTH QUEENSLAND, AUSTRALIA
David M. Colchester1,2, Gayle Webb1,
Paul Emseis2
1 Geoscience, Australian Museum, Sydney, NSW
2 School of Science, Food and Horticulture, B.C.R.I.
Campus, University of Western Sydney,
North Parramatta, NSW
ABSTRACT
Australia has appeared devoid of fossil resin occurrences except for several
very small deposits in Victoria. Recently, however, pieces of amber-like
fossil resin have been discovered on remote beaches near Cape Weymouth on
the east coast of Cape York Peninsula in North Queensland. They appear to
derive from Quaternary deposits bordering the coast. The material ranges in
colour from clear pale yellow through to dark brown and almost opaque.
Numerous inclusions are present, including fossilised insects. Tests show
specimens include both copal and amber, making them of interest to
gemmologists. FTIR spectra show the fossil resins to he broadly similar to
Baltic amber and Kauri gum (copal), but markedly different in their finer
detail.
DIAMONDS FROM THE UDACHNAYA PIPE, YAKUTIA
Their morphology, optical and Raman characterisation, FTIR and CL features
Vanda Rolandi1, Anna Brajkovic2, Ilaria Adamo3, Manuela Landonio2
1
Italian College of Gemmologists (CIG),
External Collaborator at University of Milano Bicocca, Italy
2 Department of Geological Sciences and Geotechnologies,
University of Milano Bicocca, Italy
3 Department of Earth Sciences "Ardito Desio", University of
Milano, Italy
ABSTRACT
Ten rough diamonds from the Udachnaya mine in the
Sakha Republic (Yakutia) were investigated, taking into consideration their
morphology, surface and internal features, FTIR absorption spectra and CL
topography. The diamonds ranged in weight from 0.0132 to 0.1244 grams (0.066
to 0.622 carats) and had greyish yellow to brownish orange-yellow colours.
Their most common crystal habit was a sharp edged octahedron.
Simple twinning about the central vertical plane and a pseudododecahedral habit were also present. Major surface features included growth layers, shield-shaped laminae, negatively oriented trigons and some positively oriented trigons, dislocation planes, lamination lines and etch features. Inclusions identified by stereomicroscope and Raman spectroscopy (olivine, diopside, Cr-spinel and Mg-ilmenite) indicated that eight diamonds were P-type diamonds. The presence of rutile, chromite and garnet crystals characterized two of the diamonds as E-type diamonds. Polycrystalline graphite and sulphides were detected. FTIR spectra revealed that these Udachnaya mine diamonds are type 1aAB (1aA+1aB = 100%) diamonds. CL images revealed internal textures, distribution patterns of trace elements and different growth generations. Variations in CL colour were attributed to variations in abundance of nitrogen within the diamonds. Evidence gained from colour, surface features and inclusions in these diamonds suggests that they formed at temperatures of possibly 1200 °C and pressures over 5 Gpa and were later submitted to fluctuations in temperature or pressure. The CL patterns revealed two or more differentiated growth stages in the formation of these diamonds
KRÜSS P011 PROPORTION OCULAR AND STONE HOLDER
GAA Instrument Evaluation Committee Report
T. Linton, R. Beattie, K. Hughes
ABSTRACT
The cutting proportions of diamond govern its reflected brilliance. Early in
the 20th century, Marcel Tolkowsky found that cutting facets at specific
sets of angles produced consistently bright diamonds. Proportion measuring
instruments are often used to provide information upon which reshaping of
the diamond can be based in order to improve the brightness and appeal of
the diamond. Krüss Optronics market such a proportion measuring device that
consists of proportion measuring ocular and stone holder that are used in
association with a zoom microscope.
A NEW DEPOSIT OF JERMEJEVITE FROM THE MOGOK STONE TRACT, MYANMAR
U Hla Kyi, U Kyaw Thu
Yangon, Myanmar
ABSTRACT
A number of colourless and light yellow
terminated prismatic gem quality crystals, which had a very similar
appearance to that of quartz and beryl, were purchased in Mogok. Following
detailed study these crystals were found to be jeremejevite, which is one of
the rarest gemstones found on the planet earth. This paper provides details
of the habit, crystallography, physical properties, optical properties,
microscopic characteristics, XRD and EDX-RF data for this very rare
gemstone.
FROM THE LABORATORY
Tay Thye Sun
Far East Gemological Laboratory, Singapore
ABSTRACT
Recently, two unusual items of
gemmological interest were submitted to my laboratory for identification.
This report contains a description of fake diamond crystals manufactured
from cubic zirconia, and natural ruby that has been waxed.
THE ADVERSE IMPACT OF SCATTER ON THE TONE OF SHANDONG SAPPHIRE
Li Jianjun
Shandong Provincial Gold & Gem Testing Center (SDGG)
ABSTRACT
Previous research has revealed
that dark coloured Shandong sapphire is included by large numbers of
micro-inclusions. Theoretical analysis of the results from the photometry
and colourimetry of Shandong sapphires has shown that these inclusions have
a scattering effect on the light incident on these sapphires. This
scattering greatly reduces both the transmission and internal reflection of
light from Shandong sapphire thus causing this sapphire to have a dark tone.
During heat treatment, inclusions in Shandong sapphire create fractures that
expand due thermal stress. This creates additional structural defects in
this sapphire. In addition, some structural micro-inclusions in this
sapphire increase in size during heat treatment so that they have a
scattering effect on light. As a result of this research, it has been
concluded that heat treatment can not improve the tone of Shandong sapphire.
This research also has shown that scatter has a significant deleterious
effect on the colours of gemstones
