Geochemical model of limestone silicification during glacial periods. (a) Opposite solubilities of quartz and calcite in water in relation to temperature. (b) Conceptual model of hydrological and thermal arrangements. (c) The interface between cold subsurface and warmer groundwater triggers both precipitation of silica and concomitant microkarstic dissolution of the matrix in the host limestone. Several self-organizing processes explain numerous field and petrographic characteristics of the chert layers.