Seminar

Magnesium is the second most widely occurring metal component in carbonates next only to calcium. Mg-bearing carbonate minerals play critical roles in the health of Earth system as they constitute a significant fraction of lithosphere carbon reservoir and build skeletal structures for the majority of marine invertebrate organisms. Despite the wide occurrence, high-Mg and sole-Mg phases such as dolomite ([Ca,Mg]CO3) and magnesite (MgCO3) prove to be virtually impossible to crystallize under ambient conditions. For long it is believed that Mg hydration is the culprit for this geological mystery because of the smaller size and, consequently, higher charge density of Mg2+ relative to Ca2+. The seemingly clear understanding in the role of water leads to an interesting question: will magnesite precipitate if the formation of hydration shell is breached or prevented? Meanwhile, a plethora of literature data documented the occurrence of dolomite in the presence of sulfate reducing bacteria (SRB), leaving no lucid explanation for the kinetic effect of water. The ultimate goal of our research is to address these issues through experimental testing of the following hypotheses: (1) weakened solution shell around Mg2+ will lead to MgCO3 crystallization if dehydration is the kinetic hindrance and, (2) sulfide is the ultimate mediating agent for SRB facilitated dolomite formation. Our observations indicate that there may exist a previous unrecognized and more intrinsic mineralization barrier for the formation of dolomite and magnesite at ambient conditions, and suggest that the conventional view in the inhibitory effect of water and Mg-hydration on the crystallization of Mg-containing carbonates may need to be re-evaluated.