====== The 'Dolomite Problem' ======

//Dolomite// (CaMg(CO<sub>3</sub>)<sub>2</sub>) is a ubiquitous carbonate mineral. Geologists have been debating exactly how it formed for more than two centuries. Because it's a sedimentary rock, it's clear that it was deposited in vast amounts on prehistoric seabeds.

The 'dolomitization' reaction has been resolved as :

2CaCO<sub>3</sub> + Mg<sup>2+</sup> → CaMg(CO<sub>3</sub>)<sub>2</sub> + Ca<sup>2+</sup>

But can only take place in a very limited way in modern-day seawater - so the vast deposits of dolomite cannot currently be explained. The so-called 'dolomite problem'.

It's proposed by some research groups that ancient seawater composition was very significantly different to today's. Or, that some biological process was involved (sulfate-reducing bacteria living in oxygen-free conditions may have precipitated dolomite).

Further reading [[https://en.wikipedia.org/wiki/Dolomite_(rock)#The_dolomite_problem_and_primary_dolomite|Wikipedia]]