[excerpt] Stone age craftsmen in China were polishing objects using
diamond 2,000 years before anyone else had the same idea, new evidence
suggests. Quartz was previously thought to be the abrasive used to
polish ceremonial axes in late stone age, or neolithic, China. But the
investigations of a Chinese-US team of scientists indicate that quartz
alone would not have been able to achieve such lustrous finishes.
http://news.bbc.co.uk/1/low/sci/tech/4555235.stm