cobaltoan

Cobaltoan is a mineralogical term used to describe pink to rose-red color varieties of minerals in which cobalt (Co) imparts the characteristic hue. It is an adjectival descriptor, not the name of a mineral species, and applies to several minerals whose crystal structures can accommodate cobalt.

The color mechanism involves trace cobalt substituting into the crystal lattice. In calcite, cobalt can substitute for calcium, producing what is commonly termed cobaltoan calcite. Similar cobalt-induced coloration can occur in related carbonates such as dolomite and aragonite, yielding pink varieties. Rhodochrosite can also display cobaltoan coloration when cobalt is present, resulting in pink to magenta tones. The exact shade and intensity depend on cobalt concentration and the local crystal-field environment.

Common cobaltoan varieties include cobaltoan calcite, which is the best-known example, and cobaltoan rhodochrosite. Other minerals may be described as cobaltoan if cobalt-induced coloring is evident, though these are less widespread in practice. The term serves primarily as a descriptive color label rather than a formal mineral designation.

Occurrence and formation: cobaltoan varieties arise in settings where cobalt-bearing fluids interact with carbonate or related mineral systems, such as hydrothermal veins and carbonate-hosted deposits. They can also form through secondary alteration in other rock types where cobalt is available.

In use, cobaltoan specimens are valued for distinctive pink coloration in mineral collection, and cobaltoan calcite is popular in lapidary, with consideration given to its softness and potential sensitivity to heat and light.