This small, relatively unassuming, red and green rock was found by miners in Russia and promptly donated to the country's scientific academy.
It's got 30,000 diamonds in it.
The diamonds are too small to be valuable (which goes a long way to explaining why Russia's Udachnaya diamond mine was only too happy to pass it on) at 0.04in (1mm) tall, but their concentration is around a million times greater than in typical diamond ore.
Larry Taylor, a geologist at the University of Tennessee who presented the findings at the American Geophysical Union's annual meeting in San Francisco, said: "The exciting thing for me is there are 30,000 itty-bitty, perfect octahedrons [double-pyramid shaped], and not one big diamond. It's like they formed instantaneously.
"This rock is a strange one indeed."
He said that the strange rock could help explain just how diamonds are formed.
The full findings will be presented in a special issue of Russian Geology and Geophysics next month.