Polished Crystal & Stone Eggs
How Does Rhodochrosite Form?
Rhodochrosite has the general chemical formula MnCO₃ and occurs as a result of hydrothermal activity and deposition from dissolved minerals in manganese ore deposits. Most often these deposits occur within metamorphic or sedimentary rock. Individual crystals form when manganese and carbonate ions are present within the same solution and are provided with a cavity and favorable environment for formation. These minerals can accumulate as a result of the breakdown of surrounding rocks by an aqueous solution. This solution then drips from the rock into cavities where the minerals naturally accumulate and deposit along the walls, ceiling and/or floor of the cavity. Other impurities within this solution can make their way into the crystal lattice, resulting in a variety of color hues that can range from light pink to deep red depending on the variable chemical, with some crystals bearing a brown color. In rare cases, no applicable impurities will be present within the solution, resulting in a "pure" crystal formation that is most often a rose-red color.
Generally, rhodochrosite will form as massive deposits from ascending hydrothermal fluids that fill cavities within metamorphic rock. Another rhodochrosite mass formation involves a descending aqueous solution that gathers the necessary minerals for formation, later to be deposited in open cavities within rock. This type of formation can result in stalactites (ceiling) and stalagmites (floor), assuming enough room is available for such deposition. These rhodochrosite stalactites can be found as a byproduct of silver mining, for silver and manganese are commonly found in association with each other.
Rhodochrosite fits into the isomorphic calcite group, meaning the individual crystals will present themselves with the same crystal structure. Like calcite crystals, rhodochrosite will form as rhombohedral and scalenohedral crystals, both of which cleave with three directional rhombohedral cleavage.
Where Can Rhodochrosite Be Found?
Known rhodochrosite deposits around the world include The United States (Colorado & Montana), Argentina, Peru, South Africa (Karuman), Russia, Mexico, Romania, Japan and Gabon. Due to few known locations that produce well formed crystals, these crystals when found are considered rare and quite valuable for aesthetic purposes.
One of the most well known locations that produces rhodochrosite crystals is the Sweet Home Mine in Park County, Colorado, USA. The crystals from this mine are known for their brilliant luster, color and most importantly their size. These crystals can range anywhere from microscopic up to 5+ inches! In fact, the largest documented rhodochrosite crystal discovery occurred in this mine. This rhodochrosite crystal which has since been named "Alma King", measured 5.9" across and now resides in the Denver Museum of Natural History. The discoveries of many world class specimens from this mine resulted in rhodochrosite being named the state mineral in 2002.
One of the most well known deposits of rhodochrosite stalactites and stalagmites is the Capillitas Mine in the Catamarca Province of Argentina. These accumulations of rhodochrosite that formed from precipitating minerals have become highly sought after for polished slabs and lapidary/jewelry material. This mine is considered to be the worlds largest known mass of rhodochrosite.
The history of this mining district in Argentina stretches back to the Inca Silver Mines of the area that were created around the 13-14th century. Aqueous solutions precipitating from rocks surrounding their mining tunnels began dripping through the walls and ceilings, creating stalactites and stalagmites of rhodochrosite over the centuries. These deposits resulted in banded rhodochrosite formations that have since been cut and polished, revealing the concentric rings of rhodochrosite and carbonate mineral formations.
Is Rhodochrosite The Same As Rhodonite?
Rhodochrosite and rhodonite both contain manganese which in both instances presents itself as pretty much being the same color. That being said, rhodochrosite is a manganese carbonate (MnCO₃) while rhodonite is a manganese silicate (MnSiO₃).