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Current Issue
Volume 24, Number 12, October – December 2012cover.jpg)
In this issue:
The Ellendale Diamond Field
Ellendale diamond collection at the Western Australian Museum
Non-decorative jewels
Highlights from the Giazotto mineral collection
Front Cover: Ellendale, one of only three hard-rock diamond mine locations in Australia, is a source of high-value fancy yellow diamonds. Since 2009, these highly priced stones have been marketed by Tiffany & Co. The cover illustration features three rings by Tiffany & Co. Diamond and Yellow Diamond Soleste Ring in platinum and 18k yellow gold. Diamond and Yellow Diamond Rings in platinum and 18k yellow gold. Images courtesy of Tiffany & Co.
The Ellendale Diamond Field: exploration history, discovery, geology and mining
Dr Anthony L. Ahmat
Abstract: The Ellendale Diamond Field, as one of only three hard-rock diamond mine locations in Australia, holds a unique and special place in Australia’s, and the World’s, diamond history. Although not the first diamond mine to start in Australia, Ellendale was the first hard-rock deposit to be found. On the world scene, the discovery of Ellendale led to the recognition of a new host-rock for diamond, namely lamproite, and more specifically, olivine lamproite. Up until that time, commercial-sized diamonds were considered to be sourced only from kimberlite. Within several years of the initial discovery, some 46 lamproite pipes were found at Ellendale and by 1980 thirty-eight of these pipes had been assessed for their diamond content. Over two decades later, Kimberley Diamond Company (KDC) geologists recognised eluvial diamond enrichment over these pipes and after a lengthy legal battle wrested the Ellendale Mining Lease from the AJV and commenced mining at Ellendale deposit in May 2002. Since 2002, over 2.1 million carats (Mct) of diamonds have been mined from the Ellendale 4 and 9 pipes. Ellendale is recognised as a source of high-value fancy yellow diamonds. However, the future of mining at Ellendale is tenuous. Ellendale 4 was closed in 2009, and the high Australian dollar, combined with dwindling reserves, may put pressure on the survival of Ellendale 9.
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Washed cobbles of magmatic porphyritic olivine lamproite. Photo by A.L. Ahmat. |
The Kimberley Diamond Company Ellendale diamond collection at the Western Australian Museum
Dr Peter J. Downes, Dr Alex W.R. Bevan and Dr Geoff L. Deacon
Abstract: In November 2011, the Kimberley Diamond Company and private benefactors, donated to the Western Australian Museum, a representative collection of yellow and white diamonds, to a total weight of 38.06 carats, from their operations at Ellendale in the West Kimberley region of Western Australia. The collection includes eight rough diamonds that range in weight from 0.97-3.69 carats, and in colour, from white to off-white, yellow and fancy yellow. Two specimens are diamonds in lamproite matrix, and the remainder of the collection consists of mixed parcels of small white, yellow, grey and brown uncut stones. The diamonds are predominantly resorbed, with lustrous, smooth surfaces, and include ‘dodecahedra’, irregularly-shaped stones and minor macles. Yellow colours in the Ellendale diamonds are produced by their nitrogen content that is generally in the range 100-1000 ppm. Recent estimates suggest that the Ellendale diamonds formed ~1400 Ma and were stored in a stable region of the mantle, at temperatures of 1100-1200?C, until their eruption ~22 Ma. The unusual geological setting of the Ellendale mine, hosted by olivine lamproites emplaced along the margin of the Kimberley Craton, and its production of a unique range of white and yellow diamonds, give it an important place in the natural heritage of Western Australia. The Ellendale diamond collection preserves part of this mineral heritage.
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Fine striations and pitting in the surface of a 3.69 carat fancy yellow diamond. Photo by G.L. Deacon. |
Non-decorative jewels – with particular reference to watch jewel bearings and components
John Warner
Abstract: Jewels have a near universal appeal as objects of beauty in their own right. Few people do not admire their colours and the way they transform reflected and transmitted light. The hardness and permanence of jewels can bring a lifetime of pleasure to their owners and fine jewels are much coveted. It may not be realised the extent to which jewels have a second, largely hidden, existence in which they are critical to modern civilisation. For three hundred years, jewels have been an essential component of watches in developing their ability to keep and maintain accurate time. Both mechanical and quartz watches make use of jewels that are synthesised and manufactured on a very large scale. The story of mechanical timekeeping and the importance of jewels is an interesting one, as we will discover.
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The pierced, engraved and gilded balance cock of a watch with the ruby bearing and diamond end stone; the diamond is ready to be positioned over the ruby and secured with the screws to complete the assembly. Photo by J. Warner. |
Highlights from the Giazotto Mineral Collection
Robin Hansen and Léonie Rennie
Abstract: Those of us who love gems and minerals always enjoy the opportunity to view specimens of high quality. The chance for us to do that came during a visit to Italy, where more than 500 magnificent specimens from the Giazotto Collection are on display at the Museo di Storia Naturale (Natural History Museum) in Florence. The collection, aptly titled Cristalli, L’ordine dal Caos (Crystals, Order from Chaos), was opened in March 2009.
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Part of the main gallery of the Giazotto exhibition. Photo by R. Hansen. |
