Travertine

Travertine is a continental calcareous sedimentary rock, with a concretionary appearance, more or less vacuolated, gray to yellowish, roughly bedded. 

The travertines are deposited at the emergences of certain sources, and in the not very deep rivers with small cascades (precipitation of the carbonates activated by the turbulences, and the loss in turbulences, and the loss in CO2). The current travertines are rich in aragonite, but this mineral recrystallizes then in calcite. 

The cavernous aspect is due in part to the disappearance, by fermentation, of vegetable debris encrusted with carbonates of biochemical origin (activities of blue algae). 

Certain travertines still show very beautiful prints of plants, other varieties, with vacuoles often filled with spathic calcite, are used as ornamental stone.

Photos: the Plio-Quaternary travertine of Debagh, Guelma, Algeria.