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Ancient diamond secret bared
(Xinhua)
Updated: 2005-02-18 08:22 Ancient Chinese craftsmen
might have learned to use diamonds to grind and polish ceremonial stone burial
axes as long as 6,000 years ago, US researchers said on
Wednesday.
Researchers at Harvard University have uncovered strong
evidence that the ancient Chinese used diamonds with a level of skill difficult
to achieve even with modern polishing techniques.
The finding, reported
in the February issue of the scientific journal Archaeometry, places this
earliest known use of diamond worldwide thousands of years earlier than the gem
is known to have been used elsewhere.
Scientists had put the earliest use
of diamond around 500 BC.
The latest work also represents the only known
prehistoric use of sapphire.
The stone worked into polished axes by
China's Liangzhu and Sanxingcun cultures around 4000 to 2500 BC has as its most
abundant element the mineral corundum, known as ruby in its red form and
sapphire in all other colors.
Most other known prehistoric artifacts were
fashioned from rocks and minerals no harder than quartz.
"The physics of
polishing is poorly understood. It's really more an art than a science," said
the first author Peter J. Lu. "Still, it's absolutely remarkable that with the
best polishing technologies available today, we couldn't achieve a surface as
flat and smooth as was produced 5,000 years ago."
Lu's work may
eventually yield new insights into the origins of ancient China's Neolithic
artifacts, vast quantities of finely polished jade objects.
Lu studied
four ceremonial axes, ranging in size from 13 to 22 centimeters, found at the
tombs of wealthy individuals. Three of these axes, dating to the Sanxingcun
culture of 4000 to 3800 BC and the later Liangzhu culture, came from the Nanjing
Museum in Jiangsu Province; the fourth, discovered at a Liangzhu culture site in
Zhejiang Province.
"What's most amazing about these mottled brown and
gray stones is that they have been polished to a mirror-like luster," Lu said.
"It had been assumed that quartz was used to grind the stones, but it
struck me as unlikely that such a fine finish could be the product of polishing
with quartz sand," he added.
Lu's subsequent X-ray diffraction, electron
microprobe analysis and scanning electron microscopy of the four axes'
composition gave more evidence that quartz could not have polished the stones:
fully 40 percent corundum, the second-hardest material on Earth, the only
material that could plausibly have been used to finish them so finely was
diamond.
The use of diamond by Liangzhu craftsmen is geologically
plausible, as diamond sources exist within 300 kilometers of where the burial
axes studied by Lu were found.
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