
[German Rhodochrosit, from Greek rhodokhrōs, rose-colored : rhodo-, rhodo- + khrōs, color.]
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The mineral form of manganese carbonate. Calcium, iron, magnesium, and zinc have all been reported to replace some of the manganese. The equilibrium replacement of manganese by calcium increases with the temperature of crystallization.
Rhodochrosite occurs more often in massive or columnar form than in distinct crystals. The color ranges from pale pink to brownish pink. Hardness is 3.5–4 on Mohs scale, and specific gravity is 3.70.
Well-known occurrences of rhodochrosite are in Europe, Asia, and South America. In the United States large quantities occur at Butte, Montana. As a source of manganese, rhodochrosite is also important at Chamberlain, South Dakota, and in Aroostook County, Maine. See also Carbonate minerals; Manganese.
Environment
Ore veins and metamorphic manganese deposits.
Crystal descriptionMost often in rhombohedrons (sometimes very steep), but also in scalenohedrons. Granular, massive, and in rounded spherical and botryoidal crusts.
Physical propertiesDeep rose pink to pale pink, gray, or brown. Luster vitreous to pearly; hardness 3Ɖ-4; specific gravity 3.4-3.6; fracture conchoidal; cleavage perfect rhombohedral. Brittle; transparent to translucent.
CompositionManganese carbonate (61.7% MnO, 38.3% CO 2 with any or all of the following present: iron, calcium, magnesium, zinc, and cobalt).
TestsDissolves slowly in cold and rapidly in warm hydrochloric acid with effervescence. Powder colors borax bead violet in oxidizing flame (test for manganese).
Distinguishing characteristicsThe cleavage and hardness (and acid test) show it to be a carbonate of this group. The borax bead test shows it to be a manganese mineral and eliminates about everything else. Pink color is the best guide.
OccurrenceRhodochrosite is usually a gangue mineral of copper and lead ore veins, but sometimes it occurs (like siderite) in pegmatites. At Butte, Montana, it was an ore of manganese. Commonly alters to black manganese oxides on weathering, and the black stains are very apparent on the containing rocks. Good specimens not common. Fine crystals have come from several mines (American Tunnel, Sweet Home) in Colorado, where it forms deep pink rhombohedral crystals up to several inches (10 cm) across, associated with pyrite, fluorite, quartz, and ore sulfides. Butte produced rhombohedral and scalenohedral crystals to 1 in. (2.5 cm) in crusts as well as solid cleavable and granular masses, always paler than the Colorado material, of a milky pink color. Pegmatite rhodochrosite is often grayish or brownish. Botryoidal masses and scalenohedral crystals--secondary in character, for they incrust limonite--have come from Germany (where it has been called Himbeerspat, or "raspberry spar"). Rosinca is a name applied to an Argentine occurrence of banded onyx-like pink crusts used for decorative purposes. Good but often thinly quartz-coated crystals have come from Cananea, Mexico. Hotazell, South Africa, has produced many gemmy, deep red Ɖ-1 in. (1-2 cm) crystals of an uncommonly transparent nature, which can perhaps be regarded as the most unusual specimens for collectors. Pasta Buena, Peru, has become a source of Colorado-like pink crystals with similar fluorite associations.
| Rhodochrosite | |
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Rhodochrosite from Sweet Home Mine, Alma, Colorado, USA |
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| General | |
| Category | Mineral species |
| Chemical formula | MnCO3 |
| Strunz classification | 5.AB.05 |
| Crystal symmetry | Trigonal hexagonal scalenohedral H-M symbol: (32/m) Space group: R3c |
| Unit cell | a = 4.777 Å, c = 15.67 Å; Z=6 |
| Identification | |
| Molar mass | 114.95 g/mol |
| Color | Pink, rose-red, cherry-red, yellow, yellowish gray, cinnamon-brown, may be banded |
| Crystal habit | Rhombohedral and scalenohedral crystals; also commonly bladed, columnar, stalactitic, botryoidal, granular or massive |
| Crystal system | Trigonal |
| 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 |
| Luster | 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 | [1][2][3] |
Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its (rare) pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. The streak is white. Its Mohs hardness varies between 3.5 and 4. Its specific gravity is 3.5 to 3.7. It crystallizes in the trigonal system. The cleavage is typical rhombohedral carbonate cleavage in three directions. Crystal twinning often is present. It is transparent to translucent with refractive indices of nω=1.814 to 1.816, nε=1.596 to 1.598. It is often confused with the manganese silicate, rhodonite, but is distinctly softer.
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. It is for this reason that the most common color encountered is pink.
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Rhodochrosite occurs as a hydrothermal vein mineral along with other manganese minerals in low temperature ore deposits as in the silver mines of Romania where it was first found. Banded rhodochrosite is mined in Capillitas, Argentina. Catamarca, Argentina has an old Incan silver mine that has produced fine stalactitic examples of rhodochrosite that are unique and very attractive. Cut cross-sections reveal concentric bands of light and dark rose colored layers. These specimens are carved and used for many ornamental purposes.[4]
It was first described in 1813 in reference to a sample from Cavnic, Maramureş, present-day Romania. According to Dimitrescu and Radulescu, 1966 and to Papp, 1997, this mineral was described for the first time in Sacaramb, Romania, not in Cavnic, Romania. The name is derived from the Greek word ῥοδόχρως meaning rose-colored.
Its main use is as an ore of manganese which is a key component of low-cost stainless steel formulations and certain aluminium alloys. Quality banded specimens are often used for decorative stones and jewelry. Due to its being relatively soft, and having perfect cleaveage, it is very difficult to cut, and therefore rarely found faceted in jewelry.
Manganese carbonate is extremely destructive to the amalgamation process used in the concentration of silver ores, and so until quality mineral specimens became highly sought after by collectors, they were often discarded on the mine dump.
Colorado officially named rhodochrosite as its state mineral in 2002.[5] The reason for this lies in the fact that while the mineral is found worldwide, large red crystals are found only in a few places on earth, and specimens have been found in the Sweet Home Mine near Alma, Colorado.
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| Small Rhodochrosite specimen featured in a mineral kit, from Wuton mine, Guangxi prov, China. |
The Incas believed that rhodochrosite is the blood of their former rulers, turned to stone, therefore it is sometimes called "Rosa del Inca" or "Inca Rose".[6]
| Wikimedia Commons has media related to: Rhodochrosite |
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