Silicification

Silicification is the replacement of original skeletal material accomplished through the concurrent dissolution of calcium carbonate and precipitation of silica. The processes is aided by the nucleation of silica to organic matter which surrounds the mineral crystallites within the shell. Factors that control silicification are those that influence the dissolution/precipitation process: shell mineralogy, shell ultrastructure (and, therefore, surface area), the amount and location of organic matter, and the character of the enclosing matrix. Silicification, like all types of fossilization, can produce taphonomic biases: it is far more common in Paleozoic than younger deposits, is more likely to occur in organisms with low-magnesium calcite shells, in carbonate sediments, and in environments with elevated dissolved silica.