Rhodochrosite

Authors: Sadie, Ethan, and Christian

Mineral Name: Rhodochrosite

Chemical Composition: Rhodochrosite is primarily composed of manganese carbonate (MnCO3); however, it can contain iron, magnesium, calcium, zinc, and cobalt. The chemical formula is: (Mn, Fe, Mg, Ca, Zn, Co)CO3 (7).

Color: Rhodochrosite is often pink to red but can also be brown, yellow, and grey.

Streak: White

Hardness: 3.5 - 4

Cleavage/Fracture: Like many other calcite minerals, Rhodochrosite will break with a rhombohedral cleavage, or with 3 planes that come together not at 90 degrees. Small rhombohedrons cleave off of the existing crystal (7).

Crystal Form: Similarly to the cleavage behavior, rhodochrosite exhibits both rhombohedral (rhombus-shape) crystal form and an interesting shape formation known as scalenohedra. Scalenohedral crystals are a six-sided polygon figure that resembles the famous diamond-esque hexagon; however, the main difference is that the adjoining areas, or where the pyramid bases touch each other, are diagonal towards each other instead of being level. (7). Additionally, there are other crystal forms such as botryoidal, or globular clumps with round edges, also grainy, massive, radiating, or an aggregation of crystals forming splinter-like crystals around a center point, and as veins.

Luster: Vitreous to pearly.

Special Features: Rhodochrosite is a very vivid pink, it will effervesce in the presences of hydrochloric acid, and, in its aggregate form, it shows unique bands that have a zig-zag pattern.

Varieties: Rhodochrosite has many different varieties such as Capillitite, Kutnohorite, Rosnica, Cobaltoan, Ponite, Sphaerodigaloite, and Zincorhodochrosite. Capillitite is a yellowish mineral exhibiting gray banding and contains more iron and zinc than its regular rhodochrosite (5, 7). It’s name is derived from the mine where it was first discovered, in the Catamarca province of northwest Argentina (7). Kutnohorite is an ‘intermediate’, or midway, from rhodochrosite to aragonite, another calcium carbonate mineral (5). Rosnica is a variety of rhodochrosite that, like capillitite, was also found in Catamarca (7). This variety is made of pink and white banding. The banding is in a circular form know as concentric banding. Rosnica is of the stalactic variety, meaning it is composed of long icicle-like formations (5). Cobaltoan is a co-bearing variety first reported from the Virneburg Mine in Germany (5). The Ponite variety is iron-bearing where Iron substitutes for Manganese (5). Sphareodiagolite is Rhodochrosite as minute globules in manganese ore (5). Zincorhodochrosite is a zinc-bearing variety.

Mineral Group: Rhodochrosite is a part of the calcite group of minerals, a group of carbonates that are isomorphous. Isomorphous describes two or more minerals that have the same molecular arrangement, but their specific elements are different (7). Carbonates contain one more more metallic element and also carry carbonate, CO3-.

Environment: Rhodochrosite forms from hydrothermal solutions primarily in cracks and fractures within sedimentary and metamorphic rock. Rhodochrosite can form from a calcite precipitate in certain types of mineral deposits, one of the most common being silver veins (2). Rhodochrosite can also form in layers from precipitation of highly ionic liquids containing dissolved materials (2). These materials flow downwards into the earth finding large enough cavities in which to accumulate. Over time, the rhodochrosite materials can drip from the ceiling of these cavities and onto a cavern floor, creating stalagmites and stalactites. These drips can also create the banded shapes that rhodochrosite can exhibit. This whole process is much like limestone deposits in caverns underground due to the carbonic components that make up this mineral.

Associated Rock types: Rhodochrosite is commonly associated with other carbonic minerals like dolomite that compose rock sedimentary and metamorphic rocks. Some examples of sedimentary rocks include limestone and dolostone. Metamorphic rocks include ophicarbonates, a rock containing serpentinite and carbonates, and gumberite, a metamorphosed igneous rock (7).

Occurrence in North America: Rhodochrosite has been found in several different mines located in Montana and Colorado. In Montana, mines like the former Emma Mine in Butte of Silver Bow county this mineral was found (7). In Colorado, there were several mines that reported finding large crystal forms of this mineral. Places such as the Home Sweet Home, Climax, Sunnyside, and the Mountain Monarch mines (7). The state mineral of Colorado is subsequently rhodochrosite (2).

Economic Uses: Due to its vibrant and striking pink color rhodochrosite is primarily used as an ornamental gemstone. It is not commonly used as a gemstone due to the hardness of 3.5 - 4 and the difficulty of cutting a perfect 3D cleavage plane. So items like rings and necklaces are not suitable to rhodochrosite; rather, rhodochrosite is mainly used in earrings, pendants or pins (2). The specific type of pendants are made with rhodochrosite are a cabochon. They have a round cut and are polished showing the beautiful color and, commonly, the circular patterns within the mineral.

Industrial Uses: The primary industrial usage for rhodochrosite is in manganese ore. Manganese is a commonly found metal throughout the Earth’s crust (8). Only ores containing 35% or greater of magnesense are considered commercially exploitable (8). Rhodochrosite, a carbonate ore, is one of the most important Manganese ores (8). Mining for Manganese ore is generally done in open pits. Pure Manganese is produced by hydrometallurgical and electrolytic processes (8). Manganese is rarely used by itself due to its natural hardness. It is used in various metallic alloys, one such alloy is steel (3). Manganese steel is used primarily for railroad tracks, prison bars, and gun barrels instead of normal steel because of manganese’s resistance to corrosion. (3). More specifically, manganese is a valuable alloy in steel because manganese steel oxidizes more slowly than an iron-based alloy.

First Notable Identification: Rhodochrosite was named by Johann Friedrich Ludwig Hausmann in 1813 from greek words meaning “rose” and “coloring” to describe its look (5). Intensely colored rhombohedral crystals were discovered in the Sweet Home Mine in Colorado in the 1960s (7). The Sweet Home Mine housed some of the largest rhodochrosite crystals that had ever been found. Later, in 1992, the largest rhodochrosite crystal was found in the Sweet Home Mine that was famously named the “Alma King”, a single crystal measuring 15 cm (7). It was later named the official Colorado State mineral on April 17, 2002 (6).

How We Identified It: The main feature that makes this mineral easily identifiable is its distinct color. Having a very pink and vibrant color, it is hard to miss. It also has a very angular crystal shape. This rare mineral has a very beautiful look, making it stand out when compared to other carbonates. It also has a fairly soft hardness.

Don’t Confuse It With: Rhodochrosite is actually among the minerals that are easier to identify. This is due to its distinct pink and red tones and its perfect cleavage in three directions. Because of this, it is not often confused in its appearance but in its name. The root of its name, “rhodo”, means rose colored which consequently is the root word for a lot of rose colored items like ‘rhodolite’, ‘rhodonite’ and even ‘rhododendron’ (4). So, there are many words to mix up this mineral with, the most common being ‘rhodonite’. While they are similar in color and are both associated with manganese minerals, it is fairly easy to tell them apart with the right tools (2). Rhodonite is usually associated with “black manganese oxides”, it scores much higher than rhodochrosite on Mohs hardness scale, and it will not effervesce in the presence of hydrochloric acid like rhodochrosite will (2).



Bibliography:

  1. John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, and Monte C. Nichols, Eds., Handbook of Mineralogy, Mineralogical Society of America, Chantilly, VA 20151-1110, USA. http://www.handbookofmineralogy.org/.

  2. King, Hobart M. “Rhodochrosite.” Geology, geology.com/minerals/rhodochrosite.shtml.

  3. “Manganese - Element Information, Properties and Uses | Periodic Table.” Royal Society of Chemistry - Advancing Excellence in the Chemical Sciences, www.rsc.org/periodic-table/element/25/manganese.

  4. “Rhodo-.” Dictionary.com, Dictionary.com, www.dictionary.com/browse/rhodo-.

  5. “Rhodochrosite.” Rhodochrosite: Mineral Information, Data and Localities., www.mindat.org/min-3406.html.

  6. “RHODOCHROSITE.” GemRocks: Rhodochrosite, stoneplus.cst.cmich.edu/Rhodochrosite.htm.

  7. “Rhodochrosite: The Mineral Rhodochrosite Information and Pictures.” Rhodochrosite: The Mineral Rhodochrosite Information and Pictures, www.minerals.net/mineral/rhodochrosite.aspx.

  8. Downing, James H. “Manganese Processing.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 23 Aug. 2013, www.britannica.com/technology/manganese-processing.