It can grow at about 50 cm/20 in per year.

 Tufa is the name for an unusual geological form of calcite rock.  It is not to be confused with Tuff which is volcanic. Tufa is calcium carbonate, CaCO3, formed in stalactites, stalagmites, and other deposits in limestone caves.  It forms as incrustations around mouths of hot and cold calcareous springs and along streams carrying large amounts of calcium carbonate in solution.  It also forms as relatively small, bulbous-shaped deposits where spring water seeps slowly into a lake.

 Tufa is a rough, thick, rock-like calcium carbonate deposit that forms by precipitation from bodies of water with a high dissolved calcium content.  Its porous consistency makes Tufa a perfect medium for landscaping and alpine gardening. gardens.  Calc-tuff or Tufa has the same structure but results from calcium carbonate deposits around springs and streams in some limestone areas. Undersea Tufa columns, like those in the Ikka Fjord in southwestern Greenland, that form over alkaline springs, can reach 20 m/65 ft in height and grow at about 50 cm/20 in per year.