Rhodochrosite

Rhodochrosite is a manganese carbonate, MnCO₃, belonging to the calcite group, prized for its rose-pink to deep blood-red color caused by manganese content, with iron, calcium, magnesium, and zinc substitutions producing variations toward the siderite and calcite series. It typically forms rhombohedral or scalenohedral crystals with perfect cleavage, but also occurs in botryoidal, stalactitic, granular, and massive habits, frequently found alongside quartz, fluorite, sphalerite, galena, tetrahedrite, and manganese oxides in hydrothermal veins, as well as in metasomatic and sedimentary manganese deposits.

The species' most iconic locality is Colorado's Sweet Home Mine near Alma, Park County, originally worked for silver before yielding, from the 1960s onward and especially during its 1991–2004 specimen-mining era, the world's finest gemmy red rhombohedrons, including the legendary Alma King and Alma Rose crystals now housed at the Denver Museum of Nature & Science and the Rice Northwest Museum. Other notable Colorado sources include the Climax Mine, the Sunnyside Mine in the Silverton district, the Moose Mine in Gilpin County, and the Mountain Monarch Mine near Ouray. In South Africa's Kalahari Manganese Field, the N'Chwaning Mines and Hotazel deposits near Kuruman have produced exceptional transparent-to-translucent scalenohedral crystals of deep red rhodochrosite, some facet-grade, associated with manganite and drusy quartz. Argentina's Capillitas Mine in Catamarca Province, mined since Incan times, is world-famous for banded stalactitic "Inca Rose" or "Rosa del Inca" material — the source of Argentina's national stone — showing bands from cream and yellowish-brown through the zinc-rich variety capillitite to deep crimson, later cut into cabochons, spheres, and carvings.

Other classic and collector-relevant localities include the Wolf Mine at Herdorf in Germany's Siegerland, source of botryoidal and long terminated crystals; Kapnik (Cavnic) in Romania's Baia Mare district; the Wutong Mine in Guangxi, China, known for large rhombohedral crystals; the Inakuraishi and Yakumo mines in Hokkaido, Japan; the Moanda Mine in Gabon; and Peruvian deposits at Huallapon and Uchucchacua. In the United States, Butte and Philipsburg in Montana, and Santa Eulalia in Mexico, round out the classic silver-vein occurrences where rhodochrosite was historically treated as manganese-carbonate gangue before being recognized as a collector gem. Because it ranges from vivid gemmy crystals to soft banded ornamental material, sometimes within the same deposit, rhodochrosite appeals to crystal collectors and lapidaries alike, ranking among the most desirable carbonate species and Colorado's official state mineral.