Rhodochrosite
By Bob Farrar
The Mineral of the Month for December is rhodochrosite. Named for the Greek word rhodokhros, for “of rosy color,” rhodochrosite is a beautiful and interesting mineral that is extremely popular with both mineral collectors and gem cutters. It is not, however, to be confused with rhodonite, which has a similar-soundingname and is sometimes similar in appearance.
Rhodochrosite is a carbonate, specifically, manganese carbonate, MnCO3. Within the carbonates, it is classified in the calcite group. As such, it shares many properties with calcite. For example, both minerals crystalize in the hexagonal system. The most common crystal form of rhodochrosite is the rhombohedron, but it is also found as scalenohedrons (dogtooth crystals). It can also occur as stalactitic formations, as does calcite, and as massive material. It has perfect rhombohedral cleavage, again like calcite. Where rhodochrosite differs from calcite, and what makes it so popular, though, is its color, which typically varies from various shades of pink to deep red to orange-red. Other physical properties include a hardness of 3.5 to 4, and solubility in acid. Color, crystal habit, hardness, and solubility in acid are usually sufficient to distinguish rhodochrosite. Rhodonite is much harder and insoluble in acid.Rhodochrosite typically occurs in ore veins, metamorphic manganese deposits, and pegmatites. Perhaps the finest rhodochrosite crystals ever found were mined from ore veins at the Sweet Home Mine, Alma, Colorado. Sweet Home Mine specimens are characteristically deep pink to red rhombohedrons up to 16 cm. Numerous other ore veins in Colorado have also produced good specimens, including the American Tunnel in Silverton, and, recently, the Sara Rose Mine near Alma. The Kalahari Manganese Fields of South Africa are another source of particularly fine specimens. This locality is known for intensely red, transparent scalenohedrons. Localities in Peru, Guangxi Prov., China and the Santa Eulalia area of Mexico have produced numerous specimens. An interesting occurrence is at Mt. St-Hilaire, Quebec, where it occurs as hexagonal tablets. Pegmatite occurrences of rhodochrosite are uncommon; such localities include Mt. Mica and the Bennett Mine in Maine, and Kings Mountain, North Carolina. Most gem rhodochrosite comes from the Catamarca Province of Argentina. This material occurs as stalactites that resemble onyx (calcite) stalactites in structure.
Rhodochrosite is popular as a gemstone as well as a mineral specimen. The material from Argentina is usually cabochoned, while transparent material is sometimes faceted. Faceted rhodochrosite is not common, however; it is a bit too soft, and, besides, when transparent it is usually better as a mineral specimen. Well-formed crystals of rhodochrosite of good color and any size are not common, and there is great demand for them from collectors. As a result, prices of good specimens can be very steep. However, there are enough lesser, but still nice, specimens on the market that most mineral collectors can add this wonderful mineral to their collections.
Rhodochrosite is a carbonate, specifically, manganese carbonate, MnCO3. Within the carbonates, it is classified in the calcite group. As such, it shares many properties with calcite. For example, both minerals crystalize in the hexagonal system. The most common crystal form of rhodochrosite is the rhombohedron, but it is also found as scalenohedrons (dogtooth crystals). It can also occur as stalactitic formations, as does calcite, and as massive material. It has perfect rhombohedral cleavage, again like calcite. Where rhodochrosite differs from calcite, and what makes it so popular, though, is its color, which typically varies from various shades of pink to deep red to orange-red. Other physical properties include a hardness of 3.5 to 4, and solubility in acid. Color, crystal habit, hardness, and solubility in acid are usually sufficient to distinguish rhodochrosite. Rhodonite is much harder and insoluble in acid.Rhodochrosite typically occurs in ore veins, metamorphic manganese deposits, and pegmatites. Perhaps the finest rhodochrosite crystals ever found were mined from ore veins at the Sweet Home Mine, Alma, Colorado. Sweet Home Mine specimens are characteristically deep pink to red rhombohedrons up to 16 cm. Numerous other ore veins in Colorado have also produced good specimens, including the American Tunnel in Silverton, and, recently, the Sara Rose Mine near Alma. The Kalahari Manganese Fields of South Africa are another source of particularly fine specimens. This locality is known for intensely red, transparent scalenohedrons. Localities in Peru, Guangxi Prov., China and the Santa Eulalia area of Mexico have produced numerous specimens. An interesting occurrence is at Mt. St-Hilaire, Quebec, where it occurs as hexagonal tablets. Pegmatite occurrences of rhodochrosite are uncommon; such localities include Mt. Mica and the Bennett Mine in Maine, and Kings Mountain, North Carolina. Most gem rhodochrosite comes from the Catamarca Province of Argentina. This material occurs as stalactites that resemble onyx (calcite) stalactites in structure.
Rhodochrosite is popular as a gemstone as well as a mineral specimen. The material from Argentina is usually cabochoned, while transparent material is sometimes faceted. Faceted rhodochrosite is not common, however; it is a bit too soft, and, besides, when transparent it is usually better as a mineral specimen. Well-formed crystals of rhodochrosite of good color and any size are not common, and there is great demand for them from collectors. As a result, prices of good specimens can be very steep. However, there are enough lesser, but still nice, specimens on the market that most mineral collectors can add this wonderful mineral to their collections.
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