The Dolomite Problem: A Matter of Time

Why is the mineral dolomite, CaMg(CO3)(2), abundant in ancient sedimentary rocks but scarce in modern rock-forming environments? What are the natural processes that lead to the characteristic Mg-Ca order in the dolomite structure? These important geological questions have captivated the interest of geoscientists for over a century, but the answers still remain elusive. Only recently, by the development of experimental work and the generation of large geochemical data sets, we began to suspect that both the formation and Mg-Ca ordering of dolomite could be the result of progressive dissolution-(re)crystallization reactions extended over large geological periods of time. Here, we present an initial estimate of dolomite cation-ordering times derived from previously reported data of Phanerozoic dolomites. This result provides new insight into the process of dolomite formation in nature, and it clearly suggests that can be possible to precisely determine the kinetics of the Mg- Ca ordering of natural dolomites.