Tufa

Tufa is the name for an unusual geological formation.

Tufa is a rough, thick, rock-like calcium carbonate deposit that forms by precipitation from bodies of water with a high dissolved calcium content. Tufa deposition occurs in five known ways:

• Mechanical precipitation by wave action against the shore. This form of tufa can be useful for identifying the shoreline of extinct lakes, especially 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 throughout the lake as the lake dries out
• Through the agency of algae

There are some prominent towers of Tufa at Mono Lake in California, USA