Tufas

Tufas are porous carbonate rocks formed by the precipitation of calcium carbonate from ambient-temperature water rich in dissolved calcium and bicarbonate. They develop when carbonate minerals saturate groundwater or surface seepage precipitate as the water degasses CO2 or when photosynthetic organisms raise the local pH. The result is a rock composed mainly of calcite or aragonite that can form crusts, sheets, terraces, or conical mounds.

Tufas are distinct from travertine and other speleothems, though they share chemical origins. Travertine typically forms from hot or warm springs and tends to be denser, while tufas form in cooler, near-surface waters and are often highly porous. They are commonly associated with microbial mats and algae, which can influence precipitation and create textured, layered surfaces.

They occur worldwide, especially in springs, streams, and wetland margins in carbonate-bearing regions. Notable examples include the freshwater tufa towers at Mono Lake, California, and other carbonate deposits in arid to temperate zones. Tufa formations can build extensive terraces and field-like features that record localized hydrology and biological activity over time.

In addition to their geological interest, tufas can preserve textures of microbial communities and other organic features, providing insights into past environmental conditions. They are typically not used as bulk stone in construction, though some local decorative or ornamental uses exist where exposed.