Mineral alteration
Mineral alteration refers to the various natural processes that alter a mineral's chemical composition or crystallography.
Mineral alteration is essentially governed by the laws of thermodynamics related to energy conservation, relevant to environmental conditions, often in presence of catalysts, the most common and influential being water (H2O).
The degree and scales of time in which different minerals alter vary depending on the initial product and its physical properties and susceptibility to alteration. Some minerals such as quartz and zircon are highly resistant to alteration under normal weathering conditions. Yet quartz may alter to stishovite with intense pressure, and zircon to crytolite (a metamict zircon) with amount of radioactive components and time.
In some circumstances, a mineral alters while maintaining its outer form known as a pseudomorph.
Mineral alteration is distinctly different than the rock alteration process metamorphism. It also differs from weathering. However, these processes assist in mineral alteration. Some minerals are members of a solid solution series and are samples of a range of compositional changes in a continuum, and thus are not 'mineral alteration' products.
A common oxidation example is when a natural ferrous iron mineral such as pyrite is oxidized to form goethite or other ferric iron hydroxides or sulfates.
The common mineral gypsum is a hydrous sulfate mineral that readily alters to the anhydrous sulfate aptly named anhydrite with prolonged desiccation.
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