Alex Hyde / Water cascading over naturally formed tufa dam. Tufa is a kind of limestone, formed from the precipitation of carbonate minerals which builds up around mosses and water plants to form a solid limeston...

Claudio Contreras / Hierve el Agua rock formation with calcified minerals, resembling a waterfall. Oaxaca, southern Mexico.

Graham Eaton / The Carboniferous age Limestone escaprpment of Warrendale Knotts near Settle, North Yorkshire, UK, October

David Fleetham / Red encrusting sponge (Clathria sp) on calcium carbonate-producing Seaweed / Green algae (Halimeda kanaloana). Hawaii.

Graham Eaton / A PDC (polycrystalline diamond compact) type oil field drill bit on one othe Kimmeridge ledges. Kimmeridge Bay, Dorset, UK, March. The ledges are hard Jurassic age, carbonate rich horizons of Limetone...

Pascal Tordeux / Wall formed by stream full of carbonate minerals which caused petrification, Baslieux Les Fismes, Marne, France

Pascal Tordeux / Wall formed by stream full of carbonate minerals which caused petrification, Baslieux Les Fismes, Marne, France

Floris van Breugel / Tufa towers along Mono Lake, which form as sodium carbonate reacts with calcium rich spring water. Mono Lake, California, USA. June 2017.

Floris van Breugel / Tufa towers along Mono Lake, which form as sodium carbonate reacts with calcium rich spring water. Mono Lake, California, USA. September.

Floris van Breugel / Carbonate minerals in ancient volcano north of Lake Mono, seen here at night under ultraviolet illumination. Mono Lake, California, USA. June 2017.

Floris van Breugel / Tufa towers along Mono Lake, which form as sodium carbonate reacts with calcium rich spring water. Mono Lake, California, USA. June 2017.

John Cancalosi / Leesburg conglomerate rock, a grey carbonate pebble conglomerate in a red sand-silt matrix. Leesburg , Virginia, USA.