Calcita

Calcite is a calcium carbonate (CaCO3) species of the trigonal system, very common and widely distributed in the Earth's crust.

It adopts multiple habits, including scalenohedra, prisms, laminae, and botryoidal or spherulitic aggregates. It forms in sedimentary, metamorphic or hydrothermal settings; it also precipitates as a secondary mineral in volcanic cavities, where slow cooling allows the characteristic radial fibrous growth. It shows three perfect cleavages and effervescence with acids. Fluorescence is common and is often activated by Mn2+; under UV it may emit red or pink, intense whitish-blue, or reddish tones when inclusions and natural activators are present.

Cobaltocalcite is a Co-rich variety, pink to fuchsia, typical of hydrothermal environments associated with cobalt and copper sulphides and carbonates. In the cobalt belt of the DRC, Kakanda yields magenta, flat specimens with small, bright crystals on dolomite. Campomorto produces uncommon globular habits in basaltic vesicles formed by rapid cooling, with strong contrast against the matrix. At Zimapán a range of forms occurs, including black calcite with well-defined crystals and, at Mina El Carrizal, grey crystals with intense pink or red fluorescence under UV. At Brushy Creek, marcasite and chalcopyrite commonly coat smoky scalenohedra in a two-stage growth, and at Trepča tabular or stepped aggregates on sphalerite show intense red UV fluorescence.

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