Diamonds

Diamonds require specific conditions to be created in nature, namely carbon-bearing materials must be exposed to enormous high pressure between 45 and 60 kilobars and high temperature of 1652–2372 °F (900–1300 °C). Such conditions are found only in the lithospheric mantle with the exception of meteorite strike. This kind of temperature and pressure happens only on depths estimated between 90-120 miles (140-190 km) and sometimes even deeper at the depths deeper than 300 kilometers. These conditions are only met in the thick and stable parts of continental plates, in regions of lithosphere called cratons.

How big will diamond crystal be in the end depends of the total time that diamond had for its growth and its size is proportional to time of its growth, meaning in simple terms - more time, bigger the diamond. Diamond is composed of pure carbon both from organic and inorganic carbon sources. Diamonds that originated from inorganic carbon sources are called harzburgitic diamonds and the ones from organic carbon sources are called eclogitic diamonds.

It takes a very long time for diamond to develop and diamonds that came to the Earth's surface are over 1 billion years and even more old. Diamonds can also be found in impact craters of the meteors and this tiny diamonds are called microdiamonds or nanodiamonds. This tiny diamonds are used only as indicators of ancient meteor impact sites and little bit in the industry. Diamonds are brought to the surface with the help of volcanic eruptions.

Rocks that carry diamonds are brought closer to the Earth's surface thanks to volcanic eruptions. These volcanic eruptions must have magma originating on very deep level, more than 90 miles which is three time average magma depth for most volcanoes and it doesn't happen very often. Volcanic craters of these eruptions are typically small and are extending downward in so called volcanic pipes formation. Once eruption happens these pipes are opened to the surface and then open circulation brings diamonds to the surface. Unfortunately so, not all pipes contain diamonds, and even those containing them usually have small economic profitability. Magma isn't containing diamonds, it's just a force that brings them like elevator up to the surface. Being transported to the surface, diamonds often erode out and are distributed over the large area.