Dolomite
Dolomite is a mineral CaMg(CO3)2 consisting of a calcium magnesium carbonate found in crystals and in extensive beds as a compact limestone.There is uncertainty as to the cause of its formation, as vast deposits are present in ancient rock, but it is very rarely found being produced in modern environments. This is referred to as the "Dolomite Problem". Dolomite accounts for about 10% of sedimentary rock, including much that would have been produced near the surface of the earth. However, experiments have only been able to synthesize dolomite under the high temperatures and pressures present in deeper layers.
Recent research has shown modern dolomite formation under anaerobic conditions in hypersaline lagoons along the Rio de Janeiro coast of Brazil, namely, Lagoa Vermelha and Brejo do Espinho. Similar processes have been discovered in the Coorong region of South Australia.
It is now thought to develop under these conditions only with the help of sulfate-reducing bacteria. The fact that conditions were better for the survival of these bacteria on the ancient Earth may explain the Dolomite Problem. This joins other research in pointing out many new interesting links between large-scale geology and small-scale microbiology.
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