Rhodonite

By Jorge Miramontes, Tanner Lewis, and Andrea Goodman

Mineral Name: Rhodonite

Chemical Composition: MnSiO₃

Color: Pink, Reddish brown, red

Streak: White

Hardness: 5.5-6

Cleavage/Fracture: Perfect prismatic cleavage in two directions intersecting at 90 degrees. (1)

Crystal Form: Rhodonite has a tabular and prismatic crystal form (7). It is tabular because it tends to be four sided and thin, and has a prismatic form because it usually has four sides in similar length.

Luster: The luster of rhodonite is vitreous, and less frequently pearly on cleavage surfaces.

Special Features: Rhodonite has black manganese oxide veins running through some samples and this feature gives it an appearance of pink mineral with black criss-crossing lines and flower-formations throughout. Rhodonite is also special in that it can be used as jewelry with artistic shapes or can be faceted in rare cases for a beautiful clear red jewel (1).

Varieties: There are many minerals that are included as rhodonite varieties. One of the minerals is bustamite, which is a calcium-rich variety but is considered its own mineral species (5). Fowlerite is another variety that is zinc-rich (6). Like the other two minerals, hsihutsunite is also a variety of rhodonite but this variety is calcium-rich and purple in color (6). Lastly, dyssnite is an alteration of rhodonite and contains higher valance magnesium and iron (6).

Mineral Group: Rhodonite falls in two mineral groups; silicates and inosilicates (7). It is a silicate because it contains silicon and oxygen. Rhodonite is also an inosilicate because of its form of a single chain of oxygen atoms (5).

Environment: Rhodonite is commonly found in metamorphic rocks connected with other manganese minerals. Rhodonite specifically forms in metamorphic rocks by raising the temperature within the host rock, this is called contact metamorphism. Other metamorphic rocks that can contain rhodonite are rocks that have been altered by hydrothermal metamorphism, which is chemical alterations from hot, ion-rich water. These processes occur during mountain building, which produces the greatest volume of metamorphic rock.

Associated Rock types: Metamorphic and metasomatic rocks are the rock types that contain rhodonite.(6) Rhodonite rarely is the main component in a rock, only the schist referred to as khondalite, has rhodonite as an essential component (6). Another rock that contains rhodonite as an accessory component is calc-skarn, which is a type of skarn rock (6).

Occurrence in North America: Rhodonite is found in a few small deposits across the world. In the United States you can find them North Carolina, Colorado, New Jersey, and it has also been named as the state gem of Massachusetts (1).

Economic Uses: Rhodonite in its purest form is used as an ornamental stone or gem (1). Rhodonite can also be used in items ranging from “beads, small sculptures, tumbled stones, and other lapidary projects” (1). Typically rhodonite is used as an attractive gem to appeal to the eye. Because rhodonite is low on the hardness scale, there has to be special care when carving or faceting the mineral (8). Mechanical cleaning processes are too abrasive to use on rhodonite. Instead, when cleaning your rhodonite gemstone you should use methods like a soft brush and warm water (8). Rhodonite is such a fragile gem that jewelers recommend rhodonite jewelry be stored separately, away from other, harder gemstones because the rhodonite is easily scratched (8).

Industrial Uses: Rhodonite was once used in India to extract the manganese-ore from the rock to weld on edges of axes, scythes and striking faces of hammers and heads of anvils (9). This was to harden the edges of soft iron tools (9). In very ancient times in India, the natives there would use small consumption of manganese-ore for colouring glasses and enamels (9). They would also use the manganese-ore extracted from rhodonite for imparting black and brown colours of earthenware such as tiles and glazes on teapots (9). The removal of the manganese-ore from the rhodonite consists of heating the manganese in rhodonite to its melting point of 1244 degrees celsius (10). Once the manganese is removed from the rhodonite ore, it is combined, or alloyed, with metals such as iron to make steel. It is alloyed with iron often because it removes impurities from the steel compound, like oxygen and sulfur (10).

First Notable Identification: Christoph Freidrich Jasche, a German naturalist, studying in biology, science and social science, named rhodonied in 1819 (6). The name rhodonite comes from the Greek word “rhodon”, meaning rose, because of its color.

How We Identified It: We identified this mineral for it’s popping pink and reddish colors mixed with black veins. When first seeing the mineral rhodonite you can tell it is very special because of the color pink which really stands out from the rest of the other colors within the rock sample. It can become very beautiful when made into a gemstone.

Don’t Confuse It With: Rhodonite is most commonly confused with rhodochrosite and the easiest way to tell them apart is that rhodonite is a pink/red color with veins, or roads made of black manganese oxide. Rhodochrosite is typically more pink than red with white swirls of manganese carbonate (3). Rhodonite is also harder than rhodochrosite.



Bibliography

  1. King, Hobart M. Rhodonite, Geology.com, geology.com/minerals/rhodonite.shtml. Accessed 4 Mar. 2020.

  2. "Physical and Optical Properties of Rhodonite." , 29 Dec. 2018, www.kabeeragate.com/blog/tag/rhodonite-stone/. Accessed 4 Mar. 2020.

  3. Mideaker, Tara. Healing Crystals, 9 Feb. 2019, www.healingcrystals.com/What_Is_The_Difference_Between_The_Pink_Stones_Rhondonite_And_Rhodochrosite__Articles_11875.html. Accessed 4 Mar. 2020.

  4. "Mineral Type - Rhodonite." Toprock Gemstones and Minerals, www.toprocks.com/collections/mineral-type-rhodonite?page=2. Accessed 4 Mar. 2020.

  5. "Inosilicates." Minerals.net, www.minerals.net/mineral_glossary/inosilicates.aspx. Accessed 4 Mar. 2020.

  6. Mindat.org, Mindat.org, www.mindat.org/min-3407.html#autoanchor16. Accessed 4 Mar. 2020.

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

  8. Arem, Joel E. “Rhodonite Value, Price, and Jewelry Information - Gem Society.” International Gem Society, www.gemsociety.org/article/rhodonite-jewelry-and-gemstone-information/.

  9. Pickering, W. H., and Thomas Henry Holland. Transactions of the Mining and Geological Institute of India. Mining and Geological Institute of India, 1906.

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