It's the process of atoms locking into place that produces this repeating network, this structure of carbon atoms, that eventually grows large enough that it produces crystals that we can see. As other carbon atoms move into the vicinity they will attach on. Again where the carbon is coming from, how quickly they're growing, those are all still open questions, but obviously the conditions are such that you've got some group of carbon atoms that are in close enough proximity that they start to bond. So as a result you get this hard material. That's why a diamond is such a hard material because you have each carbon atom participating in four of these very strong covalent bonds that form between carbon atoms. Because of the temperature and pressure, under these conditions, carbon atoms will bond to each other in this very strong type of bonding where each carbon atom is bonded to four other carbon atoms. What is carbon's role in forming diamonds?ĭiamonds are made of carbon so they form as carbon atoms under a high temperature and pressure they bond together to start growing crystals. Once the diamonds are brought to the surface and cooled relatively quickly, those carbon atoms are locked into place and there's just not enough energy to now start rearranging them into graphite. Once the diamonds have been brought from high temperature to low temperature very quickly-and by quickly, we mean in a matter of hours-these eruptions, these Kimberlite pipes moving to the surface, may have been traveling at rates of 20 to 30 miles per hour. And so by moving quickly they essentially got locked into place into the diamond structure. One of the things we know, therefore, about any diamonds that were brought to the surface is that the process of the Kimberlite eruption bringing the diamonds from the upper mantle to the surface of the Earth had to happen very quickly, because if they were traveling too long and too slowly they would have literally turned into graphite along the way. These are the so-called Kimberlites that are typically the sources of many of the world's mined diamonds. When the eruption reached the surface it built up a mound of volcanic material that eventually cooled, and the diamonds are contained within that. These eruptions then carried the already-formed diamonds from the upper mantle to the surface of the Earth. They were probably at a time when the earth was hotter, and that's probably why those eruptions were more deeply rooted. We haven't seen such eruptions in recent times. It's a very special kind of eruption, thought to be quite violent, that occurred a long time ago in the Earth's history. The diamonds that we see at the surface are ones then that are brought to the surface by a very deep-seated volcanic eruption. How do diamonds travel to the surface of the Earth? We don't have any way of drilling to that depth or any other way of traveling down to the upper mantle of the Earth. As far as we know, all diamonds that formed in the Earth formed under those kinds of conditions and, of course, that's a part of the Earth we can't directly sample. There's a lot of pressure, the weight of the overlying rock bearing down, so that combination of high temperature and high pressure is what's necessary to grow diamond crystals in the Earth. Obviously in that part of the Earth it's very hot. Diamonds are formed deep within the Earth about 100 miles or so below the surface in the upper mantle.
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