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Is the Earth's Mantle Full of Diamonds? (gizmodo.com)
An anonymous reader quotes a report from Gizmodo: Scientists' models show that sound waves seem to travel too quickly through the old, stable cores of continents, called "cratons," which extend deep into the mantle at depths around 120 to 150 kilometers (75 to 93 miles). Through observations, experiments, and modeling, one team figured that a potential way to explain the sound speed anomaly would be the presence of a lot of diamonds, a medium that allows for a faster speed of sound than other crystals. Perhaps the Earth is as much as 2 percent diamonds by volume, they found. Scientists have modeled the rock beneath continents through tomography, which you can think of as like an x-ray image, but using sound waves. But sound-wave velocities of around 4.7 kilometers per second (about 10,513 mph) are faster than sound-wave velocities in other kinds of minerals beneath the crust, according to the paper in the journal Geochemistry, Geophysics, Geosystems.
The researchers realized that if the regions had either 3 percent diamonds by volume or 50 percent of a rock formed at high pressure and temperature called eclogite, it would enable the sound speeds they observed. But both of those numbers seemed too high, based on observations of the minerals that end up on the Earth's surface: diamond-containing rocks called kimberlites. The researchers compromised and figured that 20 percent eclogite and 2 percent diamonds could explain the high velocities. The diamonds could be sprinkled as crystals found uniformly throughout the cratons.
The researchers realized that if the regions had either 3 percent diamonds by volume or 50 percent of a rock formed at high pressure and temperature called eclogite, it would enable the sound speeds they observed. But both of those numbers seemed too high, based on observations of the minerals that end up on the Earth's surface: diamond-containing rocks called kimberlites. The researchers compromised and figured that 20 percent eclogite and 2 percent diamonds could explain the high velocities. The diamonds could be sprinkled as crystals found uniformly throughout the cratons.
you don't start on expensive ones, you start on crappy flawed ones, it isn't expensive to learn or particularly difficult, one of my friends now does it professionally. Nowdays it is easier than ever with computers and lasers to do all the measurements to work out the best way to cut and shape it, one of the difficult skills used to be that, now that skill is barely necessary at all.