Tufa is the name for an unusual geological form of calcite rock.
Tufa is a rough, thick, rock-like calcium carbonate deposit that forms by chemical precipitation from bodies of water with a high dissolved calcium content. Tufa is not to be confused with tuff, which is volcanic.
Tufa deposition occurs in seven known ways:
- Mechanical precipitation by wave action against the shore. This form of tufa can be useful for identifying the shoreline of extinct lakes (for example in the Lake Lahontan region).
- Precipitation from supersaturated hot spring water entering cooler lake water.
- Precipitation in lake bottom sediments which are fed by hot springs from below.
- Precipitation from calcium-bearing spring water in an alkaline lake rich in carbonates.
- Precipitation throughout the lake as the lake dries out.
- Through the agency of algae. Microbial influence is often vital to tufa precipitation.
- Precipitation from cold water springs (for example in the foothills of the Rocky Mountains near Hinton, Alberta).
There are some prominent towers of tufa at Mono Lake and Trona Pinnacles in California, USA, formed by the fourth method mentioned above whilst submerged and subsequently exposed by falling water levels. Tufa is also common in Armenia.
Tufa is today occasionally shaped into a planter
. Its porous consistency makes tufa ideal for alpine gardens
. A concrete mixture called hypertufa
is used for similar purposes.