Volume 23, Number
9, January - March 2009
Grahame Brown Memorial Issue - Part One
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(Follow this link for abstracts of past issues)
The Grahame Brown Memorial Issue of the Association's journal, Part 1 is being published on the first anniversary of Grahame's death and contains personal details, photographs, reminiscences and papers authored by selected Australian authors. Grahame has touched the lives of every GAA member, whether personally, by way of his many lectures or through this journal to which he devoted so much time and effort, with dedication, enthusiasm and specialised knowledge. Because of the written word, the memory of Grahame Brown will live on for generations to come.
Grant Pearson, Editor
GRAHAME BROWN - LIST OF PUBLISHED WORKS
some personal reminiscences
the many facets of grahame brown - photo montage
sapphire - ruby characteristics west pailin, cambodia - Clues to their origin based on trace element and o isotope analysis
F.L. Sutherland1,5, G. Guiliani2, A.E.
Fallick3, M. Garland4, G. Webb5
1 School of Natural Sciences, University of Western Sydney
2 IRD UR154 LMTG Centre National de la Recherche Scientifique,
Vandoeuvre-les-Nancy, France
3 Scottish Universities Environmental Research Centre, East
Kilbride, Scotland, UK
4 420 Wilkins St London, Ontario, N6C5B2, Canada
5 Geoscience, Australian Museum, 6 College St, Sydney, NSW, 2010
Australia
ABSTRACT
Trace element (Particle-induced X-ray emission) and oxygen isotope (ß18O)
analyses on West Pailin, Cambodian sapphires and rubies further constrain
the geochernical characteristics of this basalt-derived, bimodal (two
corundum types) gem deposit. The results confirm a clear distinction between
magmatic origin sapphires (Fe 2300-8000ppm, Ti 15-1800ppm, Cr below
detection, Ga 160-260ppm; Cr/Ga < 0.01; ß18O)
7.0-7.8 0/00) and metamorphic-origin sapphires and
rubies (Fe 3300-9130ppm, Ti 60-3600ppm, Cr 160-5300ppm, Ga 28-46ppm; Cr/Ga
3.6-155;
ß18O 4.0-4.9
0/00).
Comparisons with a similar Australian bimodal corundum deposit from the
Barrington Tops, basaltic gem field show some common features, although the
West Pailin magmatic suite is more depleted in Fe and noticeably higher in
ß18O values. The metamorphic suite is more enriched in Ti and Cr
and distinctly lower in its
ß18O range than its Barrington Tops counterpart. This allows
geographic distinctions to be drawn between these bimodal corundum suites
and indicates differences in the geological processes by which corundum
crystallised under the two regions.
Key-words: Sapphire, ruby, corundum, basalt field, trace elements, oxygen isotopes, gemstone genesis, Southeast Asia, Eastern Australia.
BLUE FLUORESCENCE IN DIAMONDS
Garry Holloway
ABSTRACT
Historically 'blue white' fluorescent top coloured (D to F on the GIA colour
grading scale) diamonds were once priced around 10% more than non
fluorescent diamonds. Today, D to F coloured blue fluorescent diamonds are
usually discounted on wholesale markets. There are two main technical
reasons why fluorescent diamonds would be discounted. The diamond's body
colour may have been 'over-graded' or its transparency may have been
impaired.
There are also several possible "commercial" reasons why high coloured (DF) blue fluorescent diamonds are often discounted. For example, they may be more difficult to sell. This article will review the complex and often contradictory history.
Key-words: diamond, fluorescence, transparency, hazy, nitrogen, blue.
OPAL SIMILARITIES BETWEEN
ANDAMOOKA
AND COOBER PEDY SOUTH AUSTRALIA
I. Jack Townsend, BSC, FGAA
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ABSTRACT Many would argue that opal from Andamooka and Coober Pedy is like chalk and cheese and for much of the opal that is correct. In this paper however I would like to focus on the similarities of some of the opal from both fields and the reasons for the similarities. It is suggested that there were similar geological environments at Andamooka and at the southern Coober Pedy fields surrounding Allan Rise. |
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NATURE AND ORIGIN OF THE
ORBICULAR GRANODIORITE
FROM BOOGARDIE STATION WESTERN AUSTRALIA:
AN ORNAMENTAL STONE OF MONUMENTAL PROPORTIONS
Jennifer C. Bevan1, and Alexander W. R. Bevan2
1 E.de C. Clarke Earth Science Museum, School of Earth
and Geographical Sciences, University of Western Australia
2 Department of Earth and Planetary Sciences,
Western Australian Museum, Western Australia
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ABSTRACT An occurrence of orbicular granodiorite on Boogardie Station, West Of Mount Magnet in Western Australia is one of the oldest and largest of its kind known. The origin and development of the orbicular texture represents a complex, multi-stage series of mineral nucleation reactions, and radial and concentric growth on nucleii within the parent dioritic magma. This attractive orbicular rock has been used for a wide variety of decorative and ornamental purposes, sometimes on a grand scale. Products have included spheres, table tops, sculptures, and building materials, such as tiles. Sliced and polished individual orbicules have been used as coasters and decorative plaques. Although currently not in operation, quarrying of the deposit has occurred intermittently over the last twenty, years, and a proven lateral extension of the limited deposit may ensure production of rough material well into the future. |
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precision of instrument
readability:
your sg value may not be as good as you think it is!
Grant Pearson, Mt Waverley, Victoria
ABSTRACT
Key Words: Specific gravity, Uncertainty, readability, precision, accuracy.
