In addition to stars that may harbor colossal mines of diamond deep inside, many planets may have diamond rain down from the sky above. This is because both carbon containing gases; methane (CH4) and carbon dioxides (CO2), are common constituents in planetary atmosphere. Methane and carbon dioxide can be decomposed at high temperatures to form diamond. This is routinely practiced nowadays by a technique called chemical vapor deposition (CVD) (Fig. 1.4). In addition to high temperature decomposition of methane, high pressure may also assist in the formation of diamond. It is amazing to think that diamond raining down in
a planets' atmosphere may be as common as water raining from Earth's sky.
In addition to diamonds that may found buried deep in stars, and those that may rain down from the atmosphere on planets, diamonds are also ubiquitous in other places. Since carbon atoms exist everywhere in the universe, the frequent impact of these atoms have the potential to form diamond inevitably.
There are many ways that carbon atoms may be squeezed together to form a diamond. First, all stars and planets move relative to one another, so the act of collision between them may not uncommon. Such a collision will certainly convert the majority of carbon atoms into diamond. Second, each planet or satellite is constantly bombarded by asteroids or comets. This is why many satellites such as the moon, are covered with impact craters. Again, each meteorite impact can produce diamond dust. Indeed, nano-sized diamond particles are present in meteorites as well as in impact craters. Third, billions of asteroids and hundreds of billions of comets are constantly banging against one another. Hence, microscopic diamond may be formed in the solar system all the time. Fourth, as giant stars explode after running out of nuclear fuel (e.g. supernovae), the explosion can spew diamond debris into space. Fifth, the universe is soaked with cosmic rays, star winds, gamma ray bursts, and X-ray beams. Such energetic particles and electromagnetic radiation can convert carbon atoms into diamond. This has been proved as the absorption spectrum of diamond has been used to find atomic clusters of diamond in stellar dusts.
Coalmines could also be impregnated with diamond. For example, an old meteorite hit a coalmine in Brazil hundreds million years ago. Some of the coal was instantly melted and then quenched to form the radiant structure of amorphous diamond known as ballas. Other less hot coal was converted into a black aggregate of diamond known as carbonados. Certain uranium containing coals also contain sub-nano particles of diamond. These clusters, each containing hundreds of carbon atoms, were located along the fission tracks of disintegrated uranium nuclei. Apparently, the impact of nuclear debris against the carbon atoms in coal turned them into diamond.
In addition to the various sources of diamond mentioned, the existence of diamond is known to be deep within Earth as well. This is why volcanic mantle plumes such as kimberlite had been found to bring natural diamond up to the surface here on Earth.
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