Rhodochrosite

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Rhodochrosite
Rhodochrosite-261714.jpg
General
Category Carbonate minerals
Formula
(repeating unit)
MnCO3
Strunz classification 05.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
Formula 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. It streaks white, and its Mohs hardness varies between 3.5 and 4. Its specific gravity is between 3.5 and 3.7. It crystallizes in the trigonal system, and cleaves with rhombohedral carbonate cleavage in three directions. Crystal twinning often is present. It is transparent to translucent with refractive indices of =1.814 to 1.816, =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.

Occurrence and discovery[edit]

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.

Use[edit]

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.

Rhodochrosite and silver mining[edit]

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.

Culture and legend[edit]

Rhodochrosite is Argentina's "national gemstone".[5][6] Colorado officially named rhodochrosite as its state mineral in 2002.[7] Large specimens have been found in the Sweet Home Mine near Alma, Colorado.

Right frame 
Rhodochrosite3d.jpg
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".[8]

Gallery[edit]

See also[edit]

Manganoan Calcite

References[edit]

  1. ^ Handbook of Mineralogy
  2. ^ Rhodochrosite data on Mindat
  3. ^ Rhodochrosite data on Webmineral
  4. ^ "Rhodochrosite (Manganese Carbonate)". Amethyst Galleries, Inc. Retrieved 2007-08-15. 
  5. ^ "Piedra nacional: la Rodocrosita" (in Spanish). Embassy of the Argentine Republic in the Colombian Republic. Retrieved 7 October 2013. 
  6. ^ Moreno, María (9 November 2002). "La piedra argentina" (in Spanish). Página/12. Retrieved 7 October 2013. 
  7. ^ "Colorado State Archives; Symbols & Emblems". Retrieved 2012-02-2-.  Check date values in: |accessdate= (help)
  8. ^ R. V. Dietrich (2005-07-16). "GemRocks: Rhodochrosite". Retrieved 2007-08-15. 
  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7