also known as travertine, this rock formation occurs when dissolved calcium carbonate precipitates out of solution This is similar to the process that creates flowstone, and stalagmites and stalactites
a porous limestone formed from calcium carbonate deposited by springs Only forms underwater
A soft or porous stone formed by depositions from water, usually calcareous; called also calcareous tufa
the calcareous (chalky, containing calcium carbonate) and siliceous (flinty, containing silica) deposits of springs, lakes, or ground water; also a rock composed of compacted volcanic ash: in architectural terms, tufa refers to a rough facing stone applied to buildings to give a rustic look
Porous, moisture-retentive limestone rock, used for the cultivation of alkaline-loving, rock-dwelling alpines
A chemical sedimentary rock formed around springs and generally composed of calcium carbonate of silica