Zeolitization

Zeolitization is the diagenetic or hydrothermal alteration process in which silicate rocks and minerals, especially volcanic glass and feldspars, are transformed into zeolites, a group of hydrated aluminosilicate minerals with three-dimensional frameworks that incorporate exchangeable cations and water molecules. The transformation occurs when silica- and alumina-rich, alkaline fluids circulate through rocks, dissolving portions of the original minerals and precipitating zeolite phases in their place. This process is favored by low to moderate temperatures, typically near-surface to several hundred degrees Celsius, and by alkaline pH conditions.

Geological settings for zeolitization include volcanic ash beds and tuffs within sedimentary basins, hydrothermal veins, and altered basalts where fluids interact with feldspars and glassy volcanic material. The formation of specific zeolites depends on the precise chemical environment, particularly Si/Al ratio, alkali content, temperature, and fluid composition. Common natural zeolites formed include analcime, chabazite, clinoptilolite, mordenite, heulandite, natrolite, and stilbite.

Zeolitization affects porosity and permeability by modifying mineralogy and pore geometry, with implications for groundwater movement, reservoir quality in oil and gas geology, and contaminant behavior in the subsurface. Zeolites also have economic importance as adsorbents and catalysts in industry, and their presence in rocks serves as a diagenetic indicator of past fluid-rock interaction and thermal histories.