Whether gem grade or industrial grade, most diamonds formed under similar conditions

Science News : Some diamonds are more prized than others. Gem-quality diamonds, which tend to be billions of years old, are notable for their brilliance and lack of impurities. So-called fibrous diamonds are just millions of years old and tend to be cloudy and full of impurities. Because the two types of diamond look so different and are of such different ages, it was long thought that they must have formed under different geological conditions. However, even the most perfect diamonds contain imperfections, and those imperfections are now providing clues to the diamonds’ origins. Using a beam of electrons, researchers were able to identify tiny inclusions in diamond gemstones, which contained the same carbonate-bearing fluids found in the more fibrous diamonds. The team concluded that all diamonds must form from carbon carried deep into Earth’s interior, where it is exposed to extremely high pressures and temperatures. Furthermore, based on the age of some gemstones, the plate tectonics that carry the carbon into the planet’s interior must have started operating even earlier than previously thought, perhaps as long as 3.5 billion years ago.