Diamond-Polished Stone Age

Portions of this 5,000-year-old ceremonial burial ax are polished so well that the Stone Age craftsman must have used the hardest material on Earth.  This would move up the date by several thousand years that diamonds entered human society.

Peter Lu of Harvard University and his colleagues determined the composition of this artifact and three others from the tombs of two Neolithic Chinese cultures - the Liangzhu and the Sanxingcun.  The scientists were surprised to find that the most abundant element in the tools was the mineral corundum, which is what rubies and sapphires are made of.

Corundum is the second hardest natural material, so it is unlikely that the smoothness of the axes was due to quartz - which was originally thought to have been the polishing material.   The researchers polished samples of one ax with various abrasives and found that only diamond could come close to duplicating the ancient ax surfaces.

"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 said.

Diamond deposits within 150 miles of the burial sites may have been the source for this presumably first human use of the gem.  The findings were reported in the February issue of Archaeometry.

-- LiveScience Staff

Credit: Peter Lu