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If the solubility constant for a mineral is exceeded and, thermodynamically, a mineral is favored to precipitate in solution, are there any factors that may limit this from happening? Perhaps kinetics? Is it known if calcite precipitates out faster than dolomite does?
Also what will happen once a mineral precipitates out? Will concentrations decrease until the solution is saturated with respect to the mineral?
Thank you
This is really a wide open question on which books could be written. First let's stipulate that we are considering aqueous solutions rather than say magma.
In aqueous solution the solubility of a particular mineral depends on the temperature, pressure and chemical composition of the liquid. Generally as a solution would rise towards the surface of the earth the pressure and temperature drop which tends to decrease the solubility. Once the solution becomes saturated with respect to a certain mineral then it becomes thermodynamically favorable for the mineral to deposit. However it is possible for a solution to become supersaturated.
Also you have to remember that homogeneous conditions wouldn't really exist. There would be temperature and pressure differences in water flowing through a crevice. The water wouldn't flow at a constant rate over long periods of time. So the whole aspect of deposition and dissolution would be very dynamic.
It is also possible to dissolve minerals A and B, yet deposit some mineral C.
Also for minerals there are often many different crystal formations. Calcite deposits in hundreds of different types of crystals.
Kinetics certainly can limit precipitation of minerals from solution. This could be due to the inherently slow precipitation for a particular mineral or could be due to more rapid precipitation of another mineral (for example precipitation of aragonite from a supersaturated calcium carbonate solution, even though calcite is the more stable form at low temperatures. Catalysts or biological processes can lower the activation energy barrier for precipitation of a less thermodynamically stable phase so it precipitates faster.
It sometimes takes a significant degree of supersaturation for nucleation of mineral grains for precipitation to proceed.
These factors mean that precipitation will not always reach equilibrium between the mineral and the solution.
