Dolomitization

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.^[1] Dolomitization involves substantial amount of recrystallization. This process is described by the stoichiometric equation:^[2]

2CaCO_3(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.^[2]

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.^[1]

See also

• Dolostone
• Diagenesis

Notes

1. ^ ^{a b} Machel & Mountjoy 1986.
2. ^ ^{a b} Whitaker & Xiao 2010.

References

• Machel, Hans-G.; Mountjoy, Eric W. (May 1986), "Chemistry and Environments of Dolomitization —A Reappraisal", Earth Science Reviews 23 (3): 175–222 
• Whitaker, Fiona F.; Xiao, Yitian (June 2010), "Reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection", AAPG Bulletin, 6 94 (6): 889–917, doi:10.1306/12090909075, http://aapgbull.geoscienceworld.org/cgi/content/full/94/6/889, retrieved 4/13/2011