Calcareous sinter is a freshwater calcium carbonate deposit, also known as calc-sinter. Deposits are characterised by low porosity and well-developed lamination, often forming crusts or sedimentary rock layers. Calcareous sinter should not be confused with siliceous sinter, which the term sinter more frequently[citation needed] refers to. It has been suggested[by whom?] that the term "sinter" should be restricted to siliceous spring deposits and be dropped for calcareous deposits entirely.