Graphite outline, or a diamond within a diamond…Diamonds are formed deep in the mantle by

Graphite outline, or a diamond within a diamond…Diamonds are formed deep in the mantle by processes that are as yet little understood, but seem to involve something called mantle metasomatisation, a form of metamorphism by which the mantle is fertilised and transformed by deep circulating carbon rich fluids, resulting in the crystallisation of diamond. Analysis of ratios of carbon isotopes in some diamonds (where the enzymes used by life preferentially select for the energetically cheaper light isotope of carbon to build tissues) has shown that some of them are indeed recycled life, borne down by a subducting slab and released into the mantle fluids when the volatiles were baked and squeezed out by the tremendous forces reigning at this depth.Diamonds are then brought up to the surface by mysterious deep sourced explosions of volatile rich magma (including water and CO2) that carve and spout out through thin carrot shaped funnels called diatremes and freeze to produce a rock called Kimberlite (named after the Kimberley diamond mines of South Africa). While diamond is the form of carbon that crystallises at the pressures and temperatures in the mantle, the same process at the surface results in graphite, so any diamond on the surface is outside its stable range, but survives in this state unless it is burnt. Minerals that exist outside their formation conditions without changing (in this case reverting to graphite) are known as metastable.On their swift rise toward the surface the stones sometimes revert partially or entirely to graphite. Here we see a glimpse of the crystallisation process, in which the edges of a first generation diamond crystal overgrown by a later spurt of carbon rich fluids passing through that part of the mantle have partially reverted to tiny crystals of graphite between the two growth episodes due to a change in conditions, revealing the wonder within.LozImage credit: 1: Yixin (Jessie) Zhou 2field of view 7.19 mm:Jian Xin (Jae) Liaohttp://bit.ly/1T7H9Qu -- source link

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