"The exciting thing for me is there are 30,000 itty-bitty, perfect octahedrons, and not one big diamond. It's like they formed instantaneously," said Larry Taylor, a geologist at the University of Tennessee, Knoxville.

The concentration of diamonds in the rock is millions of times greater than that in typical diamond ore, which averages 1 to 6 carats per tonne, Taylor said.

The thousands of diamonds in the rock cluster together in a tight band, Live Science reported.

The clear crystals are just 0.04 inches tall and are octahedral, meaning they are shaped like two pyramids that are glued together at the base.

The rock has been donated to science as the diamonds' tiny size means they are worthless as gems.

Taylor said the astonishing amount of diamonds, and the rock's unusual Christmas colouring, will provide important clues to Earth's geologic history as well as the origin of these prized gemstones.

"The associations of minerals will tell us something about the genesis of this rock, which is a strange one indeed," he said.

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