Rhodochrosite

Rhodochrosite
Rhodochrosite from Sweet Home Mine, Alma, Colorado, USA
General
Category	Mineral species
Chemical formula	MnCO3
Identification
Molar mass	114.95 g/mol
Color	Red to pink, Brown to yellow, gray to white
Crystal habit	Massive to well crystaline
Crystal system	Trigonal - HexagonalScalenohedral
Twinning	on the {0112} uncommon
Cleavage	on the [1011] perfect
Fracture	uneven, conchoidal
Tenacity	brittle
Mohs Scalehardness	3.5-4
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Density	3.7 g/cm³
Optical properties	Uniaxial (-)
Birefringence	δ = 0.218
Pleochroism	weak
Ultravioletfluorescence	None

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 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.

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.^[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-dayRomania. 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 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 theSweet 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