Dictionary: rhodochrosite   (rō'də-krō'sīt')

A mineral consisting mainly of manganese carbonate, MnCO₃, light pink to rose-red in color with a pearly or vitreous luster, used as a manganese ore.

[German Rhodochrosit, from Greek rhodokhrōs, rose-colored : rhodo-, rhodo- + khrōs, color.]

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.

For more information on rhodochrosite, visit Britannica.com.

Environment

Ore veins and metamorphic manganese deposits.

Most often in rhombohedrons (sometimes very steep), but also in scalenohedrons. Granular, massive, and in rounded spherical and botryoidal crusts.

Deep 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.

Manganese carbonate (61.7% MnO, 38.3% CO ₂ with any or all of the following present: iron, calcium, magnesium, zinc, and cobalt).

Dissolves slowly in cold and rapidly in warm hydrochloric acid with effervescence. Powder colors borax bead violet in oxidizing flame (test for manganese).

The 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.

Rhodochrosite 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
Rhodochrosite from Sweet Home Mine, Alma, Colorado, USA
General
Category	Mineral species
Chemical formula	MnCO3
Identification
Molecular Weight	114.95 gm
Color	Red to pink, Brown to yellow, gray to white
Crystal habit	Massive to well crystaline
Crystal system	Trigonal - Hexagonal Scalenohedral
Twinning	on the {0112} uncommon
Cleavage	on the [1011] perfect
Fracture	uneven, conchoidal
Tenacity	brittle
Mohs Scale hardness	3.5-4
Luster	Vitreous
Optical Properties	Uniaxial (-)
Birefringence	δ = 0.218
Pleochroism	weak
Ultraviolet fluorescence	None
Streak	White
Density	3.7 gm/c3
Diaphaneity	Transparent to translucent
References	[1] [2]

Pink is the most common color of Rhodochrosite. Specimen mined near Silverton, Colorado

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 - 1.816 nε=1.596 - 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.

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 inca silver mine that has produced fine stalatitic 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.^[3]

Its main use is as an ore of manganese which is a key component of low-cost stainless steel formulations and certain alluminium 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.

It was first described in 1813 in reference to a sample from Cavnic, Maramureş, present-day Romania. The name is derived from the Greek word for rose-colored.

Colorado officially named Rhodochrosite as its state mineral in 2002 based on a proposal by a local high school (Platte Canyon High School in Bailey,Colorado). 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 some of the best specimens have been found in the Sweet Home Mine near Alma, Colorado.

The Alma King is the largest known rhodochrosite crystal; it was found in the Sweet Home Mine near Alma, Colorado. It is on display in the Denver Museum of Nature and Science.

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".^[4][5]

Rhodochrosite and Silver Mining

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.

Footnotes

1. ^ http://www.mindat.org/min-3406.html
2. ^ http://webmineral.com/data/Rhodochrosite.shtml
3. ^ Rhodochrosite (Manganese Carbonate). Amethyst Galleries, Inc.. Retrieved on 2007-08-15.
4. ^ R. V. Dietrich (2005-07-16). GemRocks: Rhodochrosite. Retrieved on 2007-08-15.
5. ^ Rhodochrosite Jewelry. LuckyGemstones.com (2007). Retrieved on 2007-08-15.

References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
• Mindat
• Webmineral data
• Mineral galleries

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