The origin of authigenic quartz in the Helvetic Siliceous Limestone (Helvetischer Kieselkalk), Switzerland

Helvetic Siliceous Limestone (Lower Cretaceous) is characterized by up to 40% of very fine (1-10 μm), evenly distributed authigenic quartz crystals. Early diagenetic dissolution of opaline sponge spicules led to silica enrichment of interstitial waters, which reprecipitated silica in the overlying horizons, forming tiny quartz crystals in pore spaces.