[meteorite-list] Volcanoes and Meteoroids Make Materials Harder Than Diamond

[Ron Baalke]

http://discovermagazine.com/2009/jul-aug/24-volcanoes-meteoroids-make-materials-harder-than-diamond    

Volcanoes and Meteoroids Make Materials Harder Than Diamond
by Adam Hadhazy
Discover Magazine
>From the July-August special issue
published online June 24, 2009


The reputation of diamond as the hardest material around is under
threat. Researchers in China and the United States recently determined
<http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000102000005055503000001&idtype=cvips&gifs=yes>
that two naturally occurring substances surpass diamond's resistance to
scratching and indentation. They calculated that the mineral
lonsdaleite - made of carbon, like diamondi - is 58 percent harder than its
famous cousin. And wurtzite boron nitride beats diamond's hardness by
about 18 percent after being subjected to pressure, which alters its
atomic bonds.

Still, in the short term diamond will continue to dominate in practical
applications such as saws, drill bits, and industrial abrasives, since
the newly studied materials are extremely rare. Lonsdaleite forms only
under the extreme pressure and heat accompanying meteorite impacts,
while wurtzite boron nitride is a by-product of intense volcanic
eruption. But scientists can create both substances in the lab, says
physicist John Janik at the Carnegie Institution for Science. Although
producing the conditions required to grow the substances in bulk remains
a challenge, Janik and others are working on synthesizing wurtzite boron
nitride and lonsdaleite to pave the way for commercial use.