Recent Finds of Aquamarine and Heliodor in Indochina

We publish courtesy of Gems & Gemology eBrief

Author: Brendan Laurs

 

In June 2010, GIA was informed by Jack Lowell (Colorado Gem & Mineral Co., Tempe, Arizona) about some attractive gem-quality crystals of aquamarine and heliodor from Indochina. According to his supplier (Tan Pham, Vietrocks.com, Philadelphia), good-quality aquamarine was mined in 2008 in northern Vietnam, from separate areas in the neighboring provinces of Thanh Hoa (in Thuong Xuan District) and Nghe An (Que Phong District). Aquamarine from Nghe An was also produced in 2003-2004. The more recent crystals range up to 20 cm long, and are notable for their saturated color. Matrix specimens (associated with smoky quartz) have been recovered only rarely, from Thanh Hoa, due to the weathered nature of the pegmatite host rocks. Clean gemstones up to approximately 35 ct have been faceted from the Vietnamese aquamarine.

Well-formed crystals of heliodor (e.g., figure 2) were recently produced from another area in Southeast Asia, which Mr. Pham suspects is Cambodia. The crystals were first noted on the market in Vietnam with a third-party source in 2007; those seen by Mr. Pham ranged up to 7.5 cm long. This heliodor, as well as the aquamarine described above, has been especially popular with Chinese buyers.

Brendan M. Laurs


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New Field Research Confirms Tibetan Andesine

We publish courtesy of Gems & Gemology eBrief

Authors: Ahmadjan AbduriyimBrendan M. Laurs

An international group traveled to Tibet in late September 2010 to investigate the controversial origin of red andesine from China. The group was organized by coauthor AA and hosted by miner Li Tong and his wife Lou Li Ping. It also included Richard Hughes (Sino Resources Mining Corp., Hong Kong), Flavie Isatelle (geologist, France), Christina Iu (M.P. Gem Corp., Kofu, Japan), Thanong Leelawatanasuk (GIT, Bangkok), Young Sze Man (Jewellery News Asia, Hong Kong), and coauthor BML. Our goal was to examine three reported Tibetan andesine localities located close to one another 90 minutes southeast of Shigatse: Bainang, Zha Lin, and Yu Lin Gu.
AA visited the Bainang mine, reportedly Tibet’s principal source of andesine, in 2008. Most of the mining there took place in 2005-2008 and was organized by Li Tong. Unfortunately, despite having official permission from the Chinese government and police escorts, a powerful local lama would not allow us to visit the deposit.

Local people using simple hand tools mined the Zha Lin deposit in 2006-2008, reportedly producing approximately 2 tonnes of andesine. We saw a series of shallow pits within the medium-gray silty soil that underlies alluvium consisting mainly of shale and mudstone. We recovered andesine from two small pits (120 cm maximum depth) we dug in the mine area, and from two out of three pits dug in random areas of undisturbed alluvium 30-50 m upslope from the mining area. As seen previously in Tibetan andesine, all the rough material was rounded and ranged from pale to deep red with a few pieces containing bluish green areas.

The Yu Lin Gu occurrence is hosted by an alluvial fan located approximately 2 km up-valley from Zha Lin. Nearly 200 kg of andesine has reportedly been picked up from the surface by locals since 2006. We recovered andesine from the surface or slightly below the surface in loose silty soil, but did not find any stones when we dug pits into the alluvial fan. The range of color and degree of rounding of these pieces were similar to those from Zha Lin, but many had less-saturated coloration.

We were unable to verify whether Yu Lin Gu is a true andesine deposit because we could not find samples at depth. Our discovery of andesine within pits dug in random, previously unexplored areas near the Zha Lin mine, however, provided proof of a genuine Tibetan andesine deposit. The original source rock for the andesine was not evident in the area, and may have previously eroded away.

Ahmadjan Abduriyim
Gemmological Association of All Japan – Zenhokyo, Tokyo

Brendan M. Laurs

Editor, Gems & Gemology, GIA Carlsbad
Note: This report may be downloaded in PDF form here

From Gems & Gemology: First Report of Cat’s-Eye Rhodonite

This article is published courtesy of  Gemological Institute of America‘s Gems & Gemology
Author: Brendan Laurs
Intellectual property: GIA
Photo by: Robert Weldon 
 

This cat’s-eye rhodonite (6.93 ct) from Brazil shows good chatoyancy. Photo by Robert Weldon.

Gems & Gemology editor Brendan Laurs prepared the following entry for the G&G Gem News International section.  

Rhodonite (MnSiO3) is an attractive pink-to-red mineral that is often sold as specimens or ornamental material, but seldom as a gemstone, since it is typically opaque and has perfect cleavage in two directions. Facetable material is very rare, and small amounts are occasionally produced from just two localities — Broken Hill, Australia, and Minas Gerais, Brazil. Some polished material has a saturated color that resembles fine spinel or rhodochrosite.

 At last month’s Gem & Jewelry Exchange show in Tucson, Luciana Barbosa (Gemological Center, Belo Horizonte, Brazil) had some attractive rhodonite cabochons showing good chatoyancy (e.g., see figure). She reported that the material was found in 2009 at Morro da Mina, near Conselheiro Lafaiete in Minas Gerais. The rhodonite is recovered as a byproduct of manganese mining, in a large open pit operated by Companhia Vale do Rio Doce. Barbosa knew of about 30 pieces of the cat’s-eye rhodonite (ranging from approximately 2 to 40 ct), and she had not seen the material previously. To her knowledge, the stones were all untreated. She indicated that the identity of the rhodonite was confirmed with X-ray diffraction analysis.
 
We believe this is the first report of cat’s-eye rhodonite.
 
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