Rhodochrosite

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Image:The Searchlight Rhodochrosite Crystal.jpg

Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO₃.

In its (rare) pure form, it is typically a rose-red colour, 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.

Rhodochrocite 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. Its main use is as an ore of manganese. 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. 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 the best specimens have been found in the Sweet Home Mine near Alma, Colorado.

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[edit] 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. Fine specimens can occasionally be found by digging through the waste piles of known localities, however, the practice is very dangerous and is often illegal.