Dolomitization
Encyclopedia
Dolomitization is a process by which dolomite
is formed when magnesium ions replace calcium ions in calcite
. It is common for this alteration into dolomite to take place due to evaporation of water in the sabkha
area. Dolomitization involves substantial amount of recrystallization. This process is described by the stoichiometric equation:
2CaCO3(limestone) + Mg2+ ↔ CaMg(CO3)2(Dolomite) + Ca2+
Dolomitization depends on specific conditions which include low Ca:Mg ratio in solution, reactant surface area, the mineralogy of the reactant, high temperatures which represents the thermodynamic stability of the system, and the presence of kinetic inhibitors like sulfate.
If the kinetic inhibitors and high temperatures are compatible then dolomitization can take place in saline environments above thermodynamic and kinetic saturation with respect to dolomite. This type of environment includes, freshwater and seawater mixing zones, normal saline to hypersaline subtidal environments, schizohaline environments and hypersaline supratidal environments. When requirements are fulfilled dolomitization can take place in alkaline environments which are those under the influence of bacterial reduction and fermentation processes, and areas with high input alkaline continental groundwaters. Environments with high temperatures (about 50°C) like subsurface and hydrothermal environments are conducive to dolomitization.
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
is formed when magnesium ions replace calcium ions in calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
. It is common for this alteration into dolomite to take place due to evaporation of water in the sabkha
Sabkha
Sabkha is a transliteration of the Arabic word for a salt flat. Sabkhas are supratidal, forming along arid coastlines and are characterized by evaporite-carbonate deposits with some siliciclastics. Sabkhas form subaerial, prograding and shoaling-upward sequences that have an average thickness of a...
area. Dolomitization involves substantial amount of recrystallization. This process is described by the stoichiometric equation:
2CaCO3(limestone) + Mg2+ ↔ CaMg(CO3)2(Dolomite) + Ca2+
Dolomitization depends on specific conditions which include low Ca:Mg ratio in solution, reactant surface area, the mineralogy of the reactant, high temperatures which represents the thermodynamic stability of the system, and the presence of kinetic inhibitors like sulfate.
If the kinetic inhibitors and high temperatures are compatible then dolomitization can take place in saline environments above thermodynamic and kinetic saturation with respect to dolomite. This type of environment includes, freshwater and seawater mixing zones, normal saline to hypersaline subtidal environments, schizohaline environments and hypersaline supratidal environments. When requirements are fulfilled dolomitization can take place in alkaline environments which are those under the influence of bacterial reduction and fermentation processes, and areas with high input alkaline continental groundwaters. Environments with high temperatures (about 50°C) like subsurface and hydrothermal environments are conducive to dolomitization.