The cleavage is rhombohedral and perfectly developed, and striations likely caused by pressure twinning are commonly evident. The luster is vitreous in general, and pearly, fibrous, or silky locally. Calcite is easily confused with kutnahorite and light-colored rhodochrosite. Calcite from the Franklin Marble fluoresces but rarely. The pink or red basic fluorescence color and its intensity vary substantially, likely as a result of compositional variation sometimes within a single hand-specimen.
Much material commonly has a very brief, slightly orange-pink phosphorescence.
Other fluorescent colors are seen locally. Composition Table 22. Chemical analyses of carbonate minerals. Calcite is a calcium carbonate mineral, polymorphous with aragonite. Physical mixtures with dolomite are common, and the analyst must be aware of these before commencing work.