Above: Examples of nephrite earrings sourced in a new study. Credit: PNAS.

        I noticed that black "flecks" often occurred within New Zealand nephrite, and these dark inclusions caught my attention.  I knew nephrite could have occasional inclusions of magnetite, pyrite, and such.  If the nephrite itself was highly variable within a single source, I wondered if these inclusions could have chemical signatures and, therefore, would be useful for sourcing.  When I examined greenstone samples using the electron microprobe, I found that the inclusions were mostly chromite, not magnetite or pyrite.  Although chromite is igneous in origin, it also occurs within metamorphic rocks because chromite withstands the high temperatures and pressures at which other minerals alter.  Trace elements in chromite may yield a useful "fingerprint" for sourcing, I concluded.

        This week, a Google News alert appeared in my email in-box -- it was a press release from Australian National University about a new study that sourced southeast-Asian nephrite using electron microprobe analysis:

Tuesday, 20 November 2007

Australian National University

Analysing the origins of jade used in ancient jewellery has revealed a trading arena that was active for more than 3,000 years and sprawled over 3,000km in Southeast Asia – possibly the largest such network discovered in the region to date.

An international research team led by archaeologists from The Australian National University used electron probe microanalysis to examine jade earrings excavated from sites all over Southeast Asia, and were able to pinpoint the origin of the precious stone to a source in Taiwan.

“People have noted the widespread use of jade in Southeast Asia since the early 20th century, so one of the big questions has been about where the stone was sourced and how it was distributed,” explained research leader Hsiao-Chun Hung, a PhD student in archaeology at ANU.

Archaeologists have long thought that the earrings were made from local jade by Austronesian peoples as they migrated and traded across Southeast Asia – but the researchers have now shown that much of the stone was sourced from Taiwan and then transported in raw form to places like the Philippines, Borneo, central Vietnam and southern Thailand – up to thousands of kilometres by sea from its source.

Team member Dr Yoshiyuki Iizuka from the Institute of Earth Sciences at the Academia Sinica in Taiwan used electron probe microanalysis to study the variable chemical composition of raw jade samples from all over Southeast Asia, building up a geographic database of the precious stone. By applying the same technique to the 144 jade artefacts, they found that 116 specimens could be traced back to Eastern Taiwan.

We know that ancient people elsewhere in the world traded over great distances,” team member Professor Peter Bellwood said. “But this is the first time that such a large trading network has been established in Southeast Asia."

Ms Hung is studying the migration of Austronesian people throughout the region to Australia’s north between 5,000 and 3,000 years ago. The researchers say their work suggests that Austronesian people, who shared a common language and resembled contemporary Southeast Asians, had a vast, complex system of trade and transportation.

ANU Media Office: Simon Couper

 

        I am happy that the grad student who led this project, Ms. Hsiao-Chun Hung, has been able to use the electron microprobe to source nephrite in Southeast Asia and that the conclusions from my exploratory research in 2002 and 2003 seems to have been supported by this new study.  I'm very pleased that analyzing the nephrite mineralogically worked so well and that chromite inclusions are indeed useful for sourcing.  Now I am looking forward to returning to sourcing New Zealand nephrite when I'm finished with my dissertation research.  I am glad to know that I was on the right track and that souring nephrite with the microprobe can actually be successful.