Scientists aren't sure how a small rock packed with more than 30,000 tiny diamonds came to be. The chunk of diamond ore was discovered in Russia's massive Udachnaya diamond mine. Because the diamonds are minuscule, they're worth little, so the mining company donated the rock to science.

Researchers in Russia and the United States have studied the rock and remain befuddled. The average piece of diamond ore boasts one to six carats per ton. The rock in question has a concentration of diamonds more than a million times greater.

Diamonds are the crystallized formation of carbon, and scientists believe they form deep in the mantle under immense pressure and high heat. Most diamond ore, it's theorized, is obliterated as the mantle's rock is rocketed to the surface by violent volcanic eruptions -- leaving only a scattering of crystals buried in Earth's crust.

Still, the more complex chemical processes of diamond formation are little understood by scientists.

"The [chemical] reactions in which diamonds occur still remain an enigma," Larry Taylor, a geologist at the University of Tennessee, told Live Science. Taylor recently presented his study of the diamond-filled rock to attendees of the American Geophysical Union's annual meeting, held in San Francisco this week.

Taylor's work with the Russian Academy of Sciences suggests the tiny diamonds formed from fluids escaped from oceanic crust during the subduction process, whereby a tectonic plate sinks into the mantle. The rock that formed the diamonds was most likely peridotite -- a dense rock composed mostly of olivine and pyroxene.

The chemical explanation is unique and unexpected, researchers say. But then again, so is the diamond ore. A more in-depth examination of the diamond is expected to be published in the next issue of the journal Russian Geology and Geophysics.