Albitization

Albitization is a metasomatic alteration process in which calcium- and potassium-rich plagioclase feldspars are replaced by albite, the sodium-rich feldspar with the composition NaAlSi3O8. It is driven by sodium-rich hydrothermal fluids that interact with feldspar-bearing rocks, leading to pervasive or patchy replacement of the original mineral by albite. The resulting texture often shows albite as a new framework with remnants of the former plagioclase preserved as irregular cores or mantling.

The alteration is common in granitoid and related hydrothermal environments and can form halos around intrusions, within shear zones, and in skarn settings. It is typically accompanied by veining and silicification, and by minerals such as quartz, calcite, chlorite, epidote, and various zeolites (for example analcime and natrolite). The process can proceed at low to intermediate temperatures and under alkaline, Na-rich fluid conditions, though exact conditions vary with rock type and fluid composition. Albitization may occur together with other alteration styles, including sericitization or karst-like dissolution in carbonate rocks.

Significance and implications include its use as a diagnostic indicator of sodium metasomatism and hydrothermal fluid flow in exploration contexts. Albitization can modify the mineralogy, chemistry, and physical properties of rocks, potentially affecting porosity and permeability and complicating radiometric dating or detailed petrographic interpretations. Globally, it is observed in a range of crustal settings associated with granitoids, hydrothermal systems, and ore-related alteration zones.