The early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine-anoxic, organic-rich sediments dominated by bacterial sulfate reduction (BSR). In such environments, bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non-stoichiometric, highly disordered and metastable (proto)dolomite. Although the boundary conditions for the formation of modern (proto)dolomites are considered to be generally understood, the role of BSR during limestone dolomitization in ancient marine environments remains questionable.