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The Gemstone Rhodochrosite
Composition: Manganese Carbonate
Crystal System: trigonal; bar 3 2/m
Hardness: 3.5 - 4
Specific Gravity: 3.5
Luster: vitreous to resinous
Color: red to pink, sometimes almost white, yellow and brown.
Cleavage: perfect in three directions
Transparency: Crystals are transparent to translucent
Associated Minerals: pyrite, fluorite, quartz, and ore sulfides calcite, ankerite, alabandite,rhodonite, bementite, spessartine, manganite
Manganese Carbonate (61.7% MnO, 38.3% CO2with any or all of the following Present: iron, calcium,magnesium, zinc and cobalt)Rhodochrosite is usually a mineral of copper and lead ore veins, but sometimes occurs, like siderite, in pegmatite's. At Butte, Montana, it is an ore of manganese. It commonly alters to black manganese oxides on weathering and the black stains are very apparent on the containing rocks. Good specimens are not common.
Pink and white banding in massive forms, non-fluorescence and specimens effervesce easily with dilute acids. The cleavage and hardness (and acid test) show it to be of the carbonate group. The borax bead test shows it to be a manganese mineral and eliminates about everything else. The pink color is the best guide.
Rhodochrosite forms in veins of copper, lead and silver which have been altered by hot water (hydro thermals), and as a secondary deposit in sedimentary layers of manganese oxide.
Crystal Habits include the rhombohedrons and scalahedrons with rounded or curved faces that can obscure the crystal shape. Some crystals can be flattened to a bladed habit and these are sometimes aggregated into rosettes or minute crystals into spherules. Also botryoidal, globular, stalactitic, layered, nodular, vein-filling and granular. Twinning is somewhat common forming penetration twins and contact twins similar to calcite's twins.
Identification of rhodochrosite is fairly easy despite a few similarly colored minerals such as rhodonite. Rhodonite is harder and has different cleavage; but perhaps the best distinguishing factor is its lack of reaction to acids. Rhodochrosite will dissolve slowly in cold, and rapidly in warm, hydrochloric acid with effervescence. Demonstrating it's carbonate chemistry. Basically, any rose-pink carbonate is considered rhodochrosite. However some calcites with a small amount of manganese impurities can be pink in color. The manganese replaces some of the calcium ions in calcite but a complete series between calcite and rhodochrosite is not established. Differentiating pink calcite from rhodochrosite may require a fluorescence test as rhodochrosite is distinctly non-fluorescent and manganese is a fluorescent activator in calcite
The famous Sweet Home Mine and American Tunnel in Colorado. The Humboldt Mine in Cochise County, Arizona. Butte, Montana, Franklin, New Jersey and many California sites. Rhodocrosite is also found in The Huaron Mine Catamarca, Argentina. Peru; Kara oba, Kazakhatan; Sacrimb, Transylvania, Romania; Cornwall, England; Harz Mountains, Germany; Tsumeb, Otavi, Namibia; Santa Eulalia and Magdalena, Mexico; N'Chwanging Mine, Hotazel, South Africa; Mont Saint-Hilaire, Quebec, Canada. Great specimens have come from the Sweet Home Mine in Colorado.
As a minor ore of manganese, an ornamental and semiprecious gemstone and as mineral specimens. Specimens. In a massive form its pink and white bands are extremely attractive and are often used in semiprecious jewelry. Rhodochrosite is often carved into figurines and tubular stalactitic forms are sliced into circles with concentric bands that are truly unique in the mineral kingdom. Fine crystals are sometimes cut into gemstones, but rhodochrosite's softness and brittleness limit it as a gemstone for everyday use.
FACTS & HISTORY:
Rhodochrosite means rose-colored The name rhodochrosite derives from the Greek words rhodos, meaning rose and khros meaning color. This is the distinctive color of most specimens although some may appear brown or light gray.
John Ghist's Earth Science class at Platte Canyon High School near Bailey, Colorado was studying rocks and minerals when they became aware that Colorado did not have a State Mineral. After some debate, the students decided that rhodochrosite, because of its red color (similar to Colorado = reddish in Spanish) should be the state mineral. They wrote a letter to State Representative Carl Miller suggesting that rhodochrosite be designated the official State Mineral. Representative Miller introduced the legislation and within three months rhodochrosite was designated the Colorado State Mineral.