The mineral rhodochrosite

Chemical Formula

MnCO₃

Composition

Manganese carbonate, sometimes containing some iron, magnesium, calcium, zinc, and cobalt. Combinations of all these elements do not exist; only particular combinations can exist. Nevertheless, the variable elements are all listed together in the "Variable Formula" field to avoid confusion. (See the Brownspar Group for more information.)

Variable Formula

(Mn,Fe,Mg,Ca,Zn,Co)CO₃

Color

Bright red, flesh, pink, orange-red, brown, gray; banded light and dark pink from one locality

Streak

White

Hardness

3½ - 4

Crystal Forms
and Aggregates

(Hexagonal) Occurs as rhombohedral and scalenohedral crystals. Dense clusters of rhombohedral crystals, as well as parallel bundles of scalenohedral crystals also occur. Other forms are botryoidal, grainy, encrusting, radiating, massive, stalactitic, and as veins.

Transparency

Transparent to translucent

Specific Gravity

3.3 - 3.6

Luster

Vitreous to pearly

Cleavage

1,3 - rhombohedral

Fracture

Conchoidal to even

Tenacity

Brittle

Other ID Marks

May darken upon exposure to air

Other Names

Inca Rose,

Raspberry Spar

Varieties

Kutnahorite - Calcium rich variety of Rhodochrosite. Formula = (Mn,Ca)CO₃

Mangansiderite - Iron rich variety of Rhodochrosite, containing a greater amount of manganese over iron. Formula = (Mn,Fe)CO₃. If the amount of manganese supercedes the iron, the mineral is now Oligonite, which is a manganese rich variety of Siderite. Formula = (Fe,Mn)CO₃.

Rosinca or Rhodochrosite Onyx - Banded, stalactitic variety of Rhodochrosite found in Catamarca, Argentina.

Capillitite - Yellowish and gray banded variety of Rhodochrosite found in Capillitas, Catamarca, Argentina, containing zinc and iron. Formula = (Mn,Zn,Fe)CO₃

In Group

Carbonates ; Calcite group

All About

Rhodochrosite belongs to the calcite group, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a partial solid solution series. All members of the calcite group crystallize in the trigonal subdivision of the hexagonal system (as rhombohedrons and scalenohedrons), have perfect rhombohedral cleavage, and exhibit a strong double refraction in transparent rhombohedrons.

When Rhodochrosite is exposed to the atmosphere, it develops a thin film of manganese oxide on its surface. This may slightly darken the color of a specimen. Rhodochrosite commonly alters into black manganese oxides (such as Pyrolusite, Manganite, and Psilomelane), and black manganese oxide stains are usually associated with Rhodochrosite.

Rhodochrosite most commonly forms in hydrothermal veins associated with silver, copper, and lead sulfides, but rarely occurs in pegmatites. A most interesting occurrence of this mineral is in Argentina, where Rhodochrosite forms stalagmites and stalactites in the ancient, 13th century Inca silver mines.
The Colorado and South African Rhodochrosite mines have produces specimens which many consider the most beautiful of all minerals. They occur in blood-red, transparent to translucent, perfectly shaped rhombohedral and scalenohedral crystals.

Uses

Rhodochrosite is faceted into cut stones, but only for collectors. However, the banded stalactitic material from Catamarca, Argentina is carved into ornaments and polished into cabochons and beads for jewelry. Fine, blood-red Rhodochrosite specimens are highly desired by collectors, and commend magnificent prices. Rhodochrosite is also used as an ore of manganese.

Striking Features

Color combined with crystal form, hardness, and cleavage

Complex Tests

Slowly effervesces and dissolves in cold hydrochloric acid, but this effect is much quicker in warm acid

Popularity (1-4)

Prevalence (1-3)

Demand (1-3)

Distinguishing
Similar Minerals

Rhodonite - harder (5½ - 6), crystallizes differently
pink Calcite - strongly effervesces in hydrochloric acid
pink Dolomite - usually in curved crystals

Commonly
Occurs With

Quartz, Chalcopyrite, Bornite, Galena, Sphalerite, Pyrite, Fluorite, Silver, Rhodonite, Limonite, Pyrolusite, Manganite, Psilomelane

Noteworthy
Localities

There are many localities where fine Rhodochrosite specimens have been obtained from:
Blood red, clear, scalenohedral crystals come from Kuruman and Hotazel, South Africa. Good specimens have also come from Kapnik, Romania and from the Wolf Mine in Siegerland, Germany. Banded Rhodochrosite stalagmites and stalactites come from the ancient silver mines of Catamarca, Argentina. Fine scalenohedral crystals were found in Peru in the Hullapon mine, Ancash, and the Huaron mine, Cerro de Pasco. In Mexico it occurs in Magdalena and Cananea, Sonora.
Much fine material also comes from the U.S. The mines yielding the most beautiful crystals are in Colorado, particularly the Sweet Home Mine near Alma, Park Co., Colorado. It originally worked for the silver it produced, but then stunning, bright red Rhodochrosite specimens started pouring out of the mine. Fine specimens have also been obtained in Colorado at the St. Elmo and Mary Murphy Mines in Chaffee Co., the Eagle Mine, Gilman Co., Leadville, Lake Co., and the Silverton mining district in San Juan Co. Large crystals and aggregates, pink in color, were found in Butte, Silver Bow Co., and Phillipsburg, Granite Co., Montana.

Picture Icon
Links

Picture Links

1. Blood-red scalenohedrons
2. Tiny rhombohedrons in rock
3. Pink, rhombohedral crystal
4. Slab of banded Rhodochrosite stalactite (cross section)
5. Rhodochrosite stalactite