Pyroxmangite

Chemical formula: Mn<sup>₂+</sup>SiO<sub>₃</sub>

A manganese silicate, a rarer polymorph of rhodonite, forming platy crystals ranging in color from pink to reddish-brown.

## Characteristics Pyroxmangite is a manganese silicate from the pyroxenoid group, a high-temperature polymorph of rhodonite. It typically forms well-developed, platy or short prismatic crystals. Its appearance is very similar to rhodonite, with which it is often confused. A characteristic feature is the tendency for superficial oxidation of manganese, which causes darkening and the formation of black coatings or spots on the crystal surface, especially along cleavage planes. ## Physical Properties Pyroxmangite's hardness on the Mohs scale is 5.5-6, making it a relatively hard mineral. It has a vitreous luster, and on cleavage planes, it can be pearly. It is transparent to translucent. Its density ranges from 3.61-3.80 g/cm³, so it is noticeably heavy. It possesses perfect cleavage in two directions. ## Colors and Varieties This mineral exhibits colors from pale pink, through intense pink and red, to reddish-brown and brown. The color depends on the iron content, which can substitute for manganese in the crystal structure. No named varieties are distinguished, and classification is based mainly on color and degree of transparency. ## History and Name The name pyroxmangite, given in 1884, refers to its similarity to minerals of the pyroxene group (due to similar cleavage angles) and to the dominant manganese in its chemical composition. It was first described based on specimens found in Ivare, Västmanland region, Sweden. ## Uses Pyroxmangite is primarily a mineral of interest to collectors. Exceptionally clear and well-colored crystals are sometimes faceted, but due to its perfect cleavage and relative rarity, these are stones intended mainly for the collector's market, not for mass-produced jewelry.

Properties

Mohs hardness: 5.5-6
Luster: Vitreous to pearly
Streak: White
Density: 3.61-3.80
Cleavage: Perfect on {110} and {1-10}
Fracture: Uneven to conchoidal
Transparency: Transparent to translucent
Crystal system: Triclinic

Diagnostic features

## Identification Helpful features in identifying pyroxmangite include its platy crystal habit, pink to reddish-brown color, vitreous luster, and occurrence in association with other manganese minerals. Black coatings of manganese oxides on the surface and along fractures are also characteristic. ## Distinguishing from Similar Minerals The biggest challenge is distinguishing pyroxmangite from rhodonite, its lower-temperature polymorph. Both minerals have almost identical chemical compositions and very similar physical properties. Definitive differentiation is almost exclusively possible using laboratory methods, such as X-ray diffraction (XRD). Visually, pyroxmangite more often forms sharply terminated, platy crystals, while rhodonite more frequently occurs as massive, granular, or rounded aggregates. Pyroxferroite, the iron analogue of pyroxmangite, is usually darker, brown or greenish-brown. ## Crystal Forms Pyroxmangite crystallizes in the triclinic system, forming platy crystals, often with a rich frontal face. Crystals can occur as single individuals or form fan-shaped and radial aggregates. It is also found in granular and massive forms.

Geological environment

## Genesis Pyroxmangite is a typical mineral of manganese-rich metamorphic rocks. It forms under conditions of regional or contact metamorphism, often in manganese ore deposits that have undergone alteration at high temperatures. It also occurs in manganese skarns and some hydrothermal veins. ## Mineral Associations This mineral often co-occurs with its polymorph, rhodonite. Other typical associated minerals include spessartine (manganese garnet), tephroite, bustamite, pyroxferroite, quartz, galena, sphalerite, and various manganese oxides. ## Localities The world's most famous pyroxmangite specimens, prized for their size and crystal quality, come from Broken Hill, New South Wales, Australia. Other important localities include the Sunnyside Mine in Colorado (USA), numerous locations in Japan (e.g., Taguchi Mine), as well as the original locality in Ivare, Sweden. It is also found in Brazil, South Africa, and Kazakhstan.

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued pyroxmangite specimens are characterized by an intense, uniform pink or red color and high transparency. Crystal habit is crucial – sharp, undamaged, platy forms are sought after. Large size of individual crystals significantly increases value. The attractiveness of a specimen is also enhanced by aesthetic placement on a rock matrix, especially in contrast with other minerals, such as quartz or galena. ## Popular Localities The deposit in Broken Hill, Australia, is considered the source of the world's best collector specimens. Crystals from there reach considerable sizes and are distinguished by excellent form and color. Specimens from the Sunnyside Mine in the USA and from Japanese localities are also highly valued by collectors, although they usually yield in size to those from Australia.

Care and storage

## Cleaning Pyroxmangite specimens should be cleaned gently, using a soft brush and distilled water. Lukewarm water with a small amount of mild soap can be used, followed by thorough rinsing. Ultrasonic cleaners should be avoided, as they can cause the mineral to cleave along its cleavage planes. ## What to Avoid The mineral is sensitive to impact and pressure due to its perfect cleavage. It should be protected from sudden temperature changes and contact with acids and strong chemicals. Prolonged exposure to humid air can accelerate the oxidation process of the surface and its darkening. ## Storage It is recommended to store specimens in a dry place, in separate, padded boxes, to avoid scratches from harder minerals. Display should protect the specimen from dust and direct, prolonged exposure to sunlight.