The Dolomite Problem: Facts, Myths and Marketing

The mineral dolomite (CaMg(CO₃)₂) and the uncertainties surrounding its origin have captivated geoscientists for over two centuries. Déodat de Dolomieu published his seminal paper on the subject in 1791, and today, the Web of Science lists 1,029 papers under the term "dolomite problem" and 27,469 under "dolomite". The essence of the “dolomite problem” lies in the paradox of this mineral's relative scarcity in modern near-surface diagenetic environments compared to its abundance in Earth’s rock record. Each year, numerous new studies are submitted that claim to have resolved the dolomite problem or, at least, to have made significant contributions toward its resolution. I disagree and argue that this controversy arises from an oversimplified understanding of calcium/magnesium carbonates, particularly regarding their formation and subsequent diagenetic pathway. Dolomite and related magnesian carbonates, including their amorphous and unordered precursors, belong to a surprisingly complex group of minerals. These minerals may be secreted from bodily fluids, induced by microbial activity, replace pre-existing carbonate minerals, or precipitate (cement) from different aqueous solutions with varying hydrogeochemical properties and temperatures, ranging from Earth's surface to low-grade metamorphic conditions at 300 °C. This diversity leads to confusion. Ancient dolomite minerals, such as those that form the regionally extensive, stratigraphically thick dolostone bodies of the Precambrian and Phanerozoic eras, often have complex petrographic histories. Consequently, the dolomite that builds these rock bodies should not be compared with the much rarer calcium/magnesium carbonates, whether they represent direct precipitates or replacement phases, collectively referred to as “dolomite” in contemporary marine diagenetic environments. Arguably, one of the most important domains for the formation and stabilisation of (replacement) dolomites is the marine pore-water realm, which can extend to burial depths of several hundred meters. Dolomite formation and stabilisation, however, continue through prograde diagenetic and metamorphic pathways over geological timescales. This raises a critical question: Is the fabric-retentive dolostone that builds ancient carbonate platforms genuinely formed nearly synchronously with sediment deposition, or is it rather a product of the (shallow to deep) burial domain, the most prolonged and arguably the least well-understood diagenetic environment? To understand the discrepancy between the scarcity of early marine diagenetic Mg/Ca carbonates and the vast dolostone rock bodies of the geological past, we must approach this question using empirical data, petrographic and crystallographic analysis, geochemical evidence, and theoretical frameworks. It is essential to avoid distorting these findings into a simplified model that creates the illusion of a problem, which might be nothing more than a myth or a marketing construct that never truly existed.