Phosphorescence of Calcite. A calcite crystal on dolomite from Penfield Quarry, Monroe County, New York. Dolomite, calcium magnesium carbonate, is a common mineral that occurs throughout the world. Thick beds of dolomite were produced by the alteration of limestones (made of calcite, calcium carbonate) by magnesium-rich hot solutions, a process called 'dolomitization'. Dolomite forms good crystals in veins in ore deposits. Crystals also occur in open spaces within massive dolomite beds. Dolomite and calcite typically form crystals with a characteristic rhomb shape. Here the sample is illuminated by visible light. Image #1 of 2 in a sequence.