Experimental crystallization of analcime zeolite from clay and feldspar precursors

Analcime is a common authigenic mineral in siliciclastic rocks and has widespread industrial applications in catalysis and ceramic production. Although its formation from volcanic glass has been extensively studied, the role of clay minerals and feldspar precursors in its genesis remains poorly constrained. This study investigates the hydrothermal formation of analcime and associated zeolites from arkosic sandstone of the Oligocene-Miocene Al Wajh Formation, northwest Saudi Arabia using Na₂CO₃ solutions (0.1 M and 0.5 M) at 80, 150, 200, and 250 °C for 336 h. The results indicate that analcime crystallized through the dissolution of feldspars, kaolinite, smectite, and illite, forming cubic to trapezohedral crystals. Mordenite and chabazite formed as minor zeolite phases at ≥ 200 °C, associated with higher silica activity and the breakdown of silica gel, smectite, and illite. Analcime precipitated as grain-coating, replacive, and pore-filling cement, with intercrystalline pores reaching up to 9.7 µm in size. The synthesised analcime may enhance the mechanical stability of the sandstone framework by reducing susceptibility to compaction. Furthermore, if exposed to acidic meteoric waters, dissolution of analcime could generate secondary intracrystalline porosity that could significantly improve the overall reservoir quality of the sandstone.