Medium-dark red, freeform step-cut pyroxmangite, 0.72-ct, 7.9 x 4.1 mm, Minas Gerais, Brazil. © The Gem Trader. Used with permission.
Pyroxmangite grains are rare, seldom clean enough to facet, and difficult to cut. However, when cut, they are extremely beautiful and rich in color.
| Data | Value |
|---|---|
| Name | Pyroxmangite |
| Crystallography | Triclinic, Crystals tabular; usually massive, in grains, cleavable. |
| Refractive Index | 1.726-1.764 |
| Colors | Reddish brown, dark brown, pale to rose pink, purplish pink. The darker colors are due to alteration. |
| Luster | Vitreous to pearly. |
| Hardness | 5.5-6 |
| Fracture | Uneven |
| Specific Gravity | 3.61-3.80 |
| Birefringence | 0.016-0.020 |
| Cleavage | Perfect 2 directions |
| Dispersion | 0.015 (C-F) |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Transparent to translucent. |
| Absorption Spectrum | Not diagnostic. |
| Formula | (Mn,Fe)SiO3. |
| Pleochroism | Slight in shades of pink and red. |
| Optics | a = 1.726-1.748; β = 1.728-1.750; γ = 1.744-1.764. Biaxial (+), 2V = 35-46°. |
| Optic Sign | Biaxial + |
| Etymology | Originally thought to be manganiferous pyroxene. |
| Occurrence | In metamorphosed rocks rich in manganese. |
Pyroxmangite: Japan (0.55). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Although pyroxmangites can show stunning transparent red colors, from reddish brown to purplish pink, these rare gems have perfect cleavage in two directions. This makes them difficult for faceters to cut and means they have great susceptibility to fracture from blows, thus, you’ll rarely see them used as jewelry stones.
Pyroxmangite forms a series with pyroxferroite. In pyroxferroites, the iron (Fe) content exceeds the manganese (Mn) content. (The pyroxmangite type material from South Carolina later proved to be pyroxferroite).
Pyroxmangites are also polymorphous with the popular gem material known as rhodonite, sharing the same chemical structure. Sometimes, they occur together.
Pyroxmangite and rhodonite (pale pink) with todorokite (black), Serrana mine, Priorat (Catalonia). Photo by Darth vader 92. Licensed under CC By-SA 4.0.
Even professional gem labs may have difficulty distinguishing pyroxmangites from rhodonites. Although rhodonites may have slightly lower refractive index (RI), birefringence, and specific gravity (SG) values, these properties as well as their colors, pleochroism, optic character, and hardness may largely overlap. Sometimes, a powder X-ray diffraction (XRD) analysis may be needed.
Scientists have synthesized pyroxmangite to study its polymorphism with rhodonite. However, there is no known jewelry use for this synthetic material.
None known.
Polished slab of massive pyroxmangite, 10.2 x 6.1 x 0.6 cm, Sunnyside Mine (American Tunnel; Mogul Mine; Washington Mine; Belle Creole; Gold Prince; Brenneman Mine; Sunnyside Mine Group), Howardsville, Silverton District, San Juan Co., Colorado. © Rob Lavinsky, www.iRocks.com. Used with permission.
Honshu, Japan and Brazil have produced gemmy material. Other notable sources include the following:
Any faceted pyroxmangites are always small, since the material is extremely scarce and available only as small transparent grains, but faceters can cut large cabochons from cleavages and massive materials. Collectors should expect to see stones up to about 2 carats.
Due to their cleavage, don’t clean pyroxmangites with mechanical systems such as ultrasonic or steam. Clean these gems only with a warm damp cloth, mild detergent, and soft brush. For more care recommendations, consult our gemstone jewelry cleaning guide.
Cherry-red pyroxmangites in matrix, 6 mm crystals, Taguchi mine, Shidara, Kita-Shidara-gun, Aichi Prefecture, Chubu Region, Honshu Island, Japan. © Rob Lavinsky, www.iRocks.com. Used with permission.
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