Metasomatism

Metasomatism is the chemical alteration of rock by fluids that add or remove elements. It can change a rock’s mineral composition while preserving much of its original texture.

Fluid–rock interaction: The exchange of matter and energy between geological fluids and solid rocks. Metasomatism is fluid–rock interaction that changes a rock’s bulk chemistry.
Metamorphism: The solid-state mineralogical and textural change of rock under new temperature, pressure, or chemical conditions. Metasomatism often accompanies metamorphism but specifically entails chemical transfer.
Skarn: A calcium- or magnesium-rich silicate rock commonly formed when fluids react with carbonate rocks near an intrusion. Skarns are prominent products of fluid-driven chemical exchange at intrusive contacts.
Potassic alteration: Hydrothermal alteration that enriches rocks in potassium-bearing minerals such as K-feldspar or biotite. It exemplifies metasomatic addition of potassium around some ore-forming systems.
Chemical potential: A thermodynamic quantity that measures how a substance’s free energy changes as its amount changes. Chemical-potential differences drive elements between fluid and rock.
Hydrothermal fluid: A hot, water-rich geological fluid that transports dissolved chemical components through the crust. Hydrothermal fluids commonly carry the elements responsible for metasomatic alteration.
Greisen: A quartz–mica rock formed by intense alteration of granitic rocks, commonly associated with tin and tungsten deposits. Greisen records late, chemically evolved fluids altering granite.
Propylitic alteration: A hydrothermal alteration assemblage commonly containing chlorite, epidote, calcite, and albite. Its mineral assemblage marks fluid-driven changes in volcanic and intrusive rocks.
Diffusion: The net movement of particles from regions of higher concentration to lower concentration. Diffusion redistributes dissolved components through minerals and along grain boundaries.
Chemical weathering: The breakdown or transformation of minerals through chemical reactions at or near Earth’s surface. It also changes rock chemistry, but usually operates through surface conditions and processes.

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