Travertine, known locally as "Banyoles stone", is a calcareous sedimentary rock used in construction. It is formed by precipitated calcium carbonate, which is carried dissolved in water. This forms layers of stone, which sometimes cover plant or animal remains, and it can look very different. Sometimes it is more rounded, such as the Oolite on display in the Lake Exhibition. In Banyoles Lake you can see some oval travertine formations, called stromatolites.