Calcite on Dolomite

The calcite crystals in this specimen from Molignon are mounted on glittering Dolomite crystals. Calcite on Dolomite is often formed during the solidification of sediment, particularly through the dolomitisation of limestone sediment. Magnesium-rich solutions replace the calcium in calcium carbonate with magnesium, giving rise to Dolomite rock. This type of rock has a smaller volume than limestone, leading to the formation of irregularly shaped cavities lined with Dolomite and calcite crystals. A famous example is the Molignonhöhle with calcite crystals of up to 50 cm in length.