Rhodochrosite is a manganese carbonate mineral. Extant analyses by Browning (1890) and Frondel and Bauer (1955) show that the studied specimens have between 75 and 95 mole % MnCO3; most are calcian. However, relatively few specimens have been analyzed, and local solid solution limits of Zn, Fe, and Mg are unstudied. Frondel and Bauer (1955) reported a local miscibility gap between calcite and rhodochrosite between 40 and 75 mole % MnCO3, but Frondel (1972) reported a solid solution series with "only a small central gap" between calcite and rhodochrosite.
Rhodochrosite was first reported from Franklin by Browning (1890). It is known from both deposits, but may have been more common at Franklin.
Rhodochrosite occurs in small (<1 cm) rhombohedral crystals which may have curved faces. It occurs as massive material, druses, late-stage coatings, and components of vein assemblages. The color is commonly strong pink but grades through light pink to nearly white, and much material may be misidentified as calcite or kutnahorite. Altered material can have a chalky appearance. Rhodochrosite cannot be reliably distinguished from kutnahorite or manganoan calcite by visual examination. Frondel and Bauer reported densities varying from 3.5-3.6 g/cm3. Rhodochrosite has a perfect rhombohedral cleavage, not always evident in fine-grained material, and a vitreous luster. There is no discernible fluorescence in ultraviolet. Rhodochrosite is best differentiated from kutnahorite using X-ray methods. Some Franklin rhodochrosite and manganoan calcite specimens were included in the thermal studies of Kulp et al. (1949).
At Franklin, rhodochrosite is known as massive material, and fine crystals occur associated with willemite and with fluorite.
The preponderance of the preserved specimen material is from veins. Rhodochrosite is a common constituent of the carbonate veins at Franklin, associated with willemite, dolomite, and serpentine and providing very attractive specimens. Frondel (1972) has noted that kutnahorite, rhodochrosite, and calcite may coexist in a single veinlet; [Dunn] has not observed this association. Some rhodochrosite occurs as the pink carbonate mineral commonly associated with pyrochroite; some of this material may be manganoan calcite.
At Sterling Hill, as at Franklin, rhodochrosite is chiefly a vein mineral, occurring commonly with willemite and with serpentine, especially in the north orebody and the lower reaches of the mine, where calcite, sphalerite, and other minerals are associated. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Year Discovered: 1813
 Formula: MnCO3
 Essential Elements: Carbon, Manganese, Oxygen
 All Elements in Formula: Carbon, Manganese, Oxygen
 IMA Status: Approved
 To find out more about this mineral at minDat's website, follow this link   Rhodochrosite

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.613

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.73

The Picking Table References
 PT Issue and PageDescription / Comment
V. 63, No. 1 – Spring 2022, pg. 20Fluorescent Rhodochrosite From the Sterling Mine, Ogdensburg, New Jersey, Earl R. Verbeek and Paul H. Shizume
View IssueV. 10, No. 2 - August 1969, pg. 11Mineral Notes - Rhodochrosite/Manganosite
View IssueV. 7, No. 2 - August 1966, pg. 13The Minerals of Sterling Hill 1962-65 by Frank Z. Edwards - Rhodochrosite

Rhodochrosite crystal sprays on Sterling Hill ore
Rhodochrosite crystal sprays (pink) on Sterling Hill ore. Non-fluorescent micro mineral, field of view about 4 mm. Photo by JVF.

Rhodochrosite, willemite crystals and minor calite from Franklin, NJRhodochrosite, willemite crystals and minor calite from Franklin, NJ under shortwave UV Light
Rhodochrosite (pink), willemite crystals (green) and minor calite from Franklin, NJ. From the collection of, and photo by Robert A. Boymistruk.
Rhodochrosite, willemite crystals and minor calite from Franklin, NJ under shortwave UV light. The willemite fluoresces green and the calcite red-orange, rhodochrosite is non-fluorescent. From the collection of, and photo by Robert A. Boymistruk.

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