What is "kieselkalk"

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.

Because of its high silica content, the Kieselkalk is much less susceptible to karstification than the overlying Schrattenkalk. In the Siebenhengste-Hohgant-Höhle cave system in Switzerland, large galleries, easily developing in the Schrattenkalk, become impenetrable fissures networks when water disappears in the Kieselkalk.