Mineral Replacement (Diagenesis)
Mechanism
Mineral replacement refers to the process whereby one mineral dissolves and another is precipitated in its place essentially simultaneously. Replacement takes place without any volume change between the replaced and replacing mineral. Delicate textures in the original mineral may, in some cases, be faithfully preserved in the replacement mineral. Well-known examples of such preserved textures can be found in petrified wood and carbonate fossils replaced by chert. [1]
Common Replacement Events
The following replacements occur in siliciclastic sedimentary rocks during burial diagenesis: [1]
- Carbonate → chert: Replacement of carbonate minerals by microcrystalline quartz (chert) [1]
- Chert → carbonate: The reverse replacement [1]
- Feldspars and quartz → carbonate: Replacement by carbonate minerals [1]
- Feldspars → clay minerals: A common mesogenetic pathway [1]
- Clay matrix → carbonate: Replacement of matrix by carbonate minerals [1]
- Calcic plagioclase → sodic plagioclase (albitization): Calcium-rich plagioclase replaced by sodium-rich plagioclase [1]
- Feldspars and volcanic rock fragments → clay or zeolite minerals: Especially common in volcaniclastic-rich sandstones [1]
Effects on Porosity and Mineralogy
Replacement may be partial or complete. Complete replacement destroys the identity of the original minerals or rock fragments, which then gives a biased impression of the rock’s original mineralogy. Replacement by clay minerals is particularly important for porosity: clay minerals tend to plug pore space and reduce permeability. Much of the clay matrix in sandstones may be produced diagenetically by the replacement of unstable framework grains. [1]
Related Topics
Clay Minerals
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Carbonate Minerals
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References & Citations
- 1.Principles of Sedimentology and Stratigraphy Boggs, Sam Jr.
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