bergartsveksling

Bergartsveksling is a geological term for the chemical exchange between rocks and their fluids, or between different components within a rock, during alteration processes. The word comes from bergart (rock) and vekseling (exchange). In practice it describes metasomatic or hydrothermal alteration in which minerals dissolve and re-precipitate as fluids move through rock, changing its mineralogy and chemical composition.

Bergartsveksling occurs in several tectonothermal settings. In contact metamorphism fluids derived from magmas alter neighboring rocks; in regional metamorphism fluids released during metamorphism migrate through large crustal volumes; in diagenetic settings, groundwater can dissolve mobile elements and re-precipitate new minerals in sediments. The dominant mechanisms are diffusion of ions across mineral-fluid interfaces, ion exchange on mineral surfaces, dissolution-precipitation reactions, and metasomatism, leading to the creation of new minerals such as clays, epidote, chlorite, and carbonate minerals.

The process can mobilize economically important metals and create alteration halos that guide ore exploration. Bergartsveksling also records geochemical signatures that help reconstruct fluid sources, temperatures, and fluid-rock interaction histories, through isotopic and trace-element analyses.

Bergartsveksling is related to, but distinct from, pure metamorphism; its defining feature is substantial chemical exchange with fluids. See also metasomatism, hydrothermal alteration, diagenesis, ore genesis.