A mystery rock containing about 30,000 diamonds has been unearthed in Russia's huge Udachnaya mine.
The rock was pulled out by workers who immediately realised it was unusual. The reddish green stone was 3mm wide and had a concentration of diamonds one million times higher than normal, Live Science reports.
Alrosa, the company that runs the diamond mine, donated the unusual find to science.
Analysis of the rock showed the diamonds inside measure just 1mm and are shaped like two pyramids stuck together.
Larry Taylor, a geologist at the University of Tennessee, presented the findings at the American Geophysical Union annual meeting: "It's like they formed instantaneously. This rock is a strange one indeed.
"The exciting thing for me is there are 30,000 itty-bitty, perfect octahedrons, and not one big diamond."
Researchers say the rock should provide information about Earth's geological history and how diamonds are formed.
"The [chemical] reactions in which diamonds occur still remain an enigma," Taylor told Live Science.
Experts believe diamonds are created deep beneath Earth's surface between the crust and the core. Volcanic eruptions can bring diamond-rich rock up to the surface, but most disintegrate on the way up, leaving the crystals intact.
The new rock is an example of a rock that survived being shot up from Earth's belly.
Researchers also say their findings suggest the diamonds crystallised from fluids that escaped from subducted oceanic crust – where one of Earth's tectonic plates slips below another.
Findings of the study will be published in January in a special issue of Russian Geology and Geophysics.