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Lacks the sparkle, but nearly as hard

Researchers at the U.S. Department of Energy's Ames Laboratory made a gem of a discovery while tinkering with an unlikely material - it's the second-hardest substance, after diamond.

By introducing a small amount of silicon into an alloy of aluminum, magnesium and boron, they created a material slightly harder than cubic boron-nitride, the material now ranked second. They call their concoction BAM - for boron, aluminum and magnesium - and hope that experiments with other additives will make it even harder.

"We think that by tweaking the composition, we may be able to push the hardness up a little higher," said Bruce Cook, lead investigator on the project.

In sample tests of BAM, the material's hardness measured at approximately 46 gigapascals (the equivalent of 6.67 million pounds per square inch), slightly higher than cubic boron-nitride's hardness of about 45 GPa. (Diamond's hardness is estimated at between 70 and 100 GPa.)

BAM could be the least expensive of the three. Cook estimated its cost at around $700 per pound, compared to cubic boron-nitride (up to $7,000 per pound) and diamond ($2,000 per pound). That could mean huge savings for manufacturers who use these types of materials in abrasives and cutting tools for grinding and machining applications.