The morphology and the growth pattern of calcium carbonate deposits formed on inner pipe surfaces, under turbulent flow, are studied. At temperatures below 30 degrees C, and for relatively high supersaturations, quite compact calcite layers are obtained, consisting of crystals growing nearly perpendicularly to the substrate surface in a columnar pattern. For small supersaturations (i.e., below a critical value S-c similar to 7), the deposition rate is drastically reduced and large isolated crystals are formed. At temperatures above 30 degrees C, rather weak dendritic aragonite patterns are dominant. The removal of magnesium from the tap water (used in the tests) results in the formation of all three polymorphs.