Synthesis of Dolomite and Geochemical Implications
- Bruce Purser,
- Maurice Tucker and
- Donald Zenger
Published Online: 14 APR 2009
Copyright © 1994 The International Association of Sedimentologists
Dolomites: A Volume in Honour of Dolomieu
How to Cite
Usdowski, E. (1994) Synthesis of Dolomite and Geochemical Implications, in Dolomites: A Volume in Honour of Dolomieu (eds B. Purser, M. Tucker and D. Zenger), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304077.ch19
- Published Online: 14 APR 2009
- Published Print: 25 MAY 1994
Print ISBN: 9780632037872
Online ISBN: 9781444304077
- petrology and geochemistry of dolomites;
- synthesis of dolomite and geochemical implications;
- dolomite question - in light of chemical interactions between carbonate minerals and aqueous solutions;
- dolomite and magnesite synthesis;
- formation of dolomite under subsurface conditions;
- sedimentary dolomite and magnesite - from precursor calcium carbonate in geochemical environment;
- dolomite formation under surface conditions;
- phase boundaries calcite- dolomite and dolomite - magnesite not known precisely
Dolomite and magnesite have been synthesized at 60°C and 90°C by the reaction of CaCO3 with saturatured CaCl2 – MgCl2 solution for periods up to 7 years. At 60C the phase boundaries of calcite–dolomite and magnesite–dolomite are at Ca2+/Mg2+ = 0.445 and 0.107, respectively. At 90°C the corresponding boundaries are at Ca2+/Mg2+ = 3.08 and 0.304.
These and previous data show that the dolomite field coincides with the Ca2+/Mg2+ ratios of the majority of subsurface solutions at about 120°C. It follows that the probability of ‘burial’ dolomitization by an encounter between migrating pore solutions and carbonate sediments increases with increasing temperature. The Ca2+/Mg2+ ratios of the most abundant solutions and the boundary of calcite-dolomite suggest that the most frequent temperatures of ‘burial’ dolomitization are between 80°C and 90°C.
Mineral assemblages and compositions of solutions from sabkha- type environments reflect specific reaction paths. The evaporation of seawater and other solutions provides low Ca2+/Mg2+ ratios and high ionic strengths, so that the resulting brines are located in either the dolomite or the magnesite field. Thus, precursor calcium carbonate may react to dolomite and magnesite or to metastable equivalents. However, as reaction rates are slow, sufficient time has to be provided. From the assemblage dolomite + magnesite the Ca2+/Mg2+ ratio of the phase boundary may be obtained. The assemblage Mg–calcite + protodolomite is ambiguous.