Extended data
Formation principle
Diamonds are the products of diamond processing. Diamonds are the hardest and simplest gems in the world. It is a cubic natural crystal composed of carbon.
Its composition is basically the same as our common coal, pencil lead and sugar. Under high temperature and pressure, carbon element crystallizes to form graphite (black), while under high temperature, extremely high pressure and reducing environment (usually anoxic environment), it crystallizes to become precious diamond (colorless).
Since the discovery of diamonds in India, some people have found diamonds on rivers and beaches. This is because the original rock containing diamonds located in the upper reaches of the river is weathered and broken, and the diamonds are taken to the downstream zone with the water flow, and the heavier diamonds are buried in the gravel.
1870, diamonds were dug up in the loess of a farm in South Africa. After that, the excavation of diamonds moved from the river bed to the loess. Below the loess is a hard dark blue rock, which is the original stone of diamonds-kimberlite.
Kimberlite is an alkaline ultrabasic volcanic rock, which is formed in the deep part of the earth and contains a lot of volatile components such as carbonic acid gas. This kind of rocks often contain peridotite and eclogite fragments from the deep earth, and the main mineral components are olivine, phlogopite, carbonate, pyroxene and garnet.
The study shows that kimberlite magma was formed in the deep part of the earth below 150 km. Because this rock was first discovered in Kimberly, South Africa, it was named after this place name.
Another kind of original rock containing diamonds is called K-Mg lamprophyre, which is an overbased magnesian volcanic rock. It is mainly formed by leucite and volcanic glass, and may contain minerals such as pyroxene and olivine. Its typical origin is argyle, Western Australia.