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Researchers have found shock-synthesized hexagonal diamonds on one of California's Channel Islands, which they say is the strongest evidence yet that a comet exploded in the atmosphere above North America, causing widespread extinctions there around 12,900 years ago... In 2007 researchers theorized that a comet set off continental fires that led to the mysterious disappearance of the Clovis people and the extermination of 35 mammal genera, including mammoths, mastodons, ground sloths and camels. The team documented a "black mat" of charcoal throughout North America that contains high levels of iridium, magnetic spheres, and nano-diamonds, which are consistent with such an...

The reputation of diamond as the hardest material around is under threat. Researchers in China and the United States recently determined that two naturally occurring substances surpass diamond’s resistance to scratching and indentation. They calculated that the mineral lonsdaleite—made of carbon, like diamond—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....