Kieselkalk
（重定向自Siliceous limestone）
Kieselkalk is also known as the Helvetic Siliceous Limestone. It has sedimented during the Lower Cretaceous epoch. It can contain up to 40% of very fine (1-10 μm), evenly distributed authigenic quartz crystals. Early diagenetic dissolution of opal sponge spicules led to silica enrichment of interstitial waters, which reprecipitated silica in the overlying horizons, forming tiny quartz crystals in pore spaces.