A new study says diamonds are about as common as dirt. Researchers from M.I.T. say they've found a quadrillion tons of diamonds buried below the surface of the Earth. That's a thousand times more than a trillion. The researchers say this diamond abundance won't lead to deep discounts at jewelry stores. That's because the diamond deposits are buried about 90 to 150 miles below the Earth's surface, and that's a lot deeper than current mining machinery can dig. The scientists found the maybe-not-so-precious stones with the kind of seismic technology used to measure earthquakes.