Cobaltocalcite

Cobaltocalcite, more correctly termed cobaltoan calcite, is a vividly pink-to-rose-red variety of calcite in which cobalt (Co²⁺) substitutes for calcium within the (Ca,Co)CO₃ lattice. As a member of the calcite group, it shares calcite's trigonal symmetry, perfect rhombohedral cleavage and Mohs hardness of 3, but the cobalt chromophore gives it a saturated magenta-pink color unmatched among common carbonates. It is frequently confused in the trade with the much rarer spherocobaltite, the true cobalt end-member carbonate (CoCO₃), and with cobalt-bearing dolomite sold under the trade name "Salrose"; genuine cobaltocalcite is calcium-dominant, while spherocobaltite is cobalt-dominant and typically shows deeper raspberry to crimson tones.

The most important source of fine cobaltocalcite specimens today is the Bou Azzer mining district in Morocco's Anti-Atlas, particularly the Agoudal Mine and Aghbar Mine, where lustrous pink druzy crusts and sharp rhombohedral crystals form in association with cobaltite, skutterudite, chalcopyrite and malachite within the world's richest cobalt-nickel arsenide deposit. The species was originally described from the Cape Calamita Mine on Elba Island, Italy, and important cobalt-carbonate material is also mined in the Katanga Copperbelt of the Democratic Republic of Congo, notably at the Musonoi Mine, Mashamba West Mine and Kakanda deposit near Kolwezi, alongside associated heterogenite, dolomite and kolwezite. Older European occurrences include the historic cobalt veins of Schneeberg in Saxony, Germany, classic ground for cobalt-arsenide and cobalt-carbonate mineralogy.

Collectors prize cobaltocalcite for its intense, almost unnatural bubblegum-pink to rose-red coloration, its typical botryoidal, druzy or scalenohedral habit, and its relative scarcity compared to ordinary color varieties of calcite, since cobalt-rich hydrothermal environments are geologically uncommon. Fine Moroccan pieces combine gemmy, highly lustrous crystals with striking contrast against dark host matrix, making them popular both as aesthetic display specimens and as reference pieces for the calcite-spherocobaltite series. Because true cobaltoan calcite, cobaltoan dolomite and spherocobaltite are easily confused, well-documented, correctly labeled specimens from known localities such as Bou Azzer or Kolwezi carry particular value for systematic mineral collections and for studying cobalt substitution chemistry in carbonate minerals.