| Rhodochrosite | |
|---|---|
 | |
| General | |
| Category | Carbonate minerals |
| Formula (repeating unit) | MnCO3 |
| IMA symbol | Rds[1] |
| Strunz classification | 5.AB.05 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) |
| Space group | R3c |
| Unit cell | a = 4.777, c = 15.67 [Å]; Z = 6 |
| Identification | |
| Formula mass | 114.95 g/mol |
| Color | Pink, rose, rose-red, red, cherry-red, yellow, yellowish grey, grey, cinnamon-brown, white, may be banded; colourless to pale rose in transmitted light. |
| Crystal habit | Rhombohedral and scalenohedral crystals; also commonly bladed, columnar, stalactitic, botryoidal, granular or massive |
| Twinning | On {1012} as contact and lamellar |
| Cleavage | On {1011} perfect; parting on {1012} |
| Fracture | Uneven, conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 3.5–4 |
| Lustre | Vitreous to pearly |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.7 |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.814–1.816 nε = 1.596–1.598 |
| Birefringence | δ = 0.218 |
| Pleochroism | weak |
| Ultraviolet fluorescence | None |
| References | [2][3][4] |
Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its pure form (rare), it is typically a rose-red colour,[5] but it can also be shades of pink to pale brown. It streaks white,[6] and its Mohs hardness varies between 3.5 and 4.5. Its specific gravity is between 3.45 and 3.6.[7] The crystal system of rhodochrosite is trigonal, with a structure and cleavage in the carbonate rhombohedral system. The carbonate ions (CO2−
3) are arranged in a triangular planar configuration, and the manganese ions (Mn2+) are surrounded by six oxygen ions in an octahedral arrangement. The MnO6 octahedra and CO3 triangles are linked together to form a three-dimensional structure. Crystal twinning is often present. It can be confused with the manganese silicate rhodonite, but is distinctly softer.[8] Rhodochrosite is formed by the oxidation of manganese ore, and is found in South Africa, China, and the Americas.[6] It is one of the national symbols of Argentina and the state of Colorado.
Rhodochrosite forms a complete solid solution series with iron carbonate (siderite). Calcium (as well as magnesium and zinc, to a limited extent) frequently substitutes for manganese in the structure, leading to lighter shades of red and pink, depending on the degree of substitution. This is the reason for the rose color of rhodochrosite.
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2003). "Rhodochrosite". Handbook of Mineralogy (PDF). Vol. V (Borates, Carbonates, Sulfates). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209740.
- ^ Rhodochrosite. Mindat.org
- ^ Rhodochrosite. Webmineral
- ^ Deer, William Alexander (1998). Rock-forming Minerals: Non-Silicates. Vol. 5B. Geological Society of London. pp. 150–152. ISBN 9781897799901.
- ^ a b Cairncross, Bruce (2015). Understanding Minerals & Crystals. Penguin Random House South Africa. p. 180. ISBN 9781775843344.
- ^ Ridgway, Robert Henderson (1933). Manganese: General Information. U.S. Department of the Interior, Bureau of Mines. p. 3.
- ^ Rhodonite. Mindat.org