Pyrosmalite-(Mn)

Chemical formula: Mn₂+₈Si₆O₁₅(OH,Cl)₁₀

A manganese silicate forming characteristic tabular, pseudohexagonal crystals with a pearly luster.

## Characteristics Pyrosmalite-(Mn) is a mineral from the pyrosmalite group, being a hydrated manganese silicate with an admixture of chlorine. It forms characteristic, well-developed crystals with a tabular habit and hexagonal outline, although it crystallizes in the trigonal system. Crystals often occur as rosetted or radial aggregates, as well as in granular and lamellar masses. The basal surfaces of the crystals (cleavage planes) exhibit a distinct pearly luster, while other faces may be vitreous or greasy. ## Physical Properties The mineral's hardness on the Mohs scale is 4.5, classifying it as a relatively soft material. It is brittle and exhibits perfect cleavage in one plane, parallel to the crystal base. Its density ranges from 3.06-3.19 g/cm³. The mineral is usually translucent, becoming opaque in thicker fragments or in darker varieties. ## Colors and Varieties The most common colors are shades of brown, from pale yellowish-brown to reddish-brown and almost black. It also occurs in grayish-green and gray colors. Pyrosmalite-(Mn) forms an isomorphic series with pyrosmalite-(Fe), in which iron predominates over manganese. Depending on the Mn:Fe ratio, the color and other physical properties may vary slightly. ## History and Name The name "pyrosmalite" comes from the Greek words *pyr* (πῦρ) meaning "fire" and *osme* (ὀσμή) meaning "smell". It refers to the characteristic odor emitted by the mineral when heated. The suffix "-(Mn)" was added in 1982 by the International Mineralogical Association (IMA) to distinguish the manganese member of the series from its iron counterpart, pyrosmalite-(Fe). ## Uses Pyrosmalite-(Mn) has no industrial applications. However, it is a valued and sought-after collector's mineral, especially specimens from classic localities such as Franklin in the USA or Broken Hill in Australia.

Properties

Mohs hardness: 4.5
Luster: Pearly to Vitreous or Greasy
Streak: Pale brown
Density: 3.06-3.19
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features of pyrosmalite-(Mn) are its tabular, pseudohexagonal crystal habit, perfect cleavage in one direction, and pearly luster on cleavage planes. Its occurrence in paragenesis with other manganese minerals is also characteristic. ## Distinguishing from similar minerals Pyrosmalite-(Mn) is sometimes confused with minerals of similar habit and luster, such as micas (e.g., biotite, muscovite) or friedelite. - It differs from micas by its greater hardness (4.5 compared to 2.5-3 for micas), less elastic lamellae, and different chemical composition. - Friedelite, although often co-occurring with pyrosmalite, usually has more globular or spherulitic aggregates and a different crystal structure. - Pyrosmalite-(Fe) is visually almost identical, and certain differentiation requires chemical analysis. ## Crystal Forms Crystals are usually thick- or thin-tabular, with a distinct hexagonal outline. They often form aggregates of parallel-grown crystals, as well as fan-shaped and rosetted masses. It also occurs in lamellar, granular, or massive forms.

Geological environment

## Genesis Pyrosmalite-(Mn) is a mineral typical of metamorphosed, stratiform manganese and zinc ore deposits. It forms under conditions of contact and regional metamorphism. It is also found in manganese skarns. ## Mineral Associations This mineral often co-occurs with other manganese minerals and silicates. In the Franklin and Sterling Hill deposits (USA), its typical associated minerals include franklinite, willemite, rhodochrosite, tephroite, rhodonite, and calcite. In Broken Hill (Australia), it occurs in association with galena, sphalerite, rhodonite, and quartz. ## Localities The most important and well-known localities worldwide, from which the best specimens of pyrosmalite-(Mn) originate, are the mines in the Franklin and Sterling Hill area in New Jersey, USA. Other significant occurrences include Broken Hill in New South Wales (Australia), Långban and Nordmark in Sweden, and the Wafangzi mine in Liaoning Province, China.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens of pyrosmalite-(Mn) are characterized by sharp, well-formed crystals with a distinct hexagonal outline. Large, single crystals or aesthetic rosettes on a contrasting matrix (e.g., on white calcite) are particularly sought after. The intensity and shade of the brown color also affect attractiveness, as does a strong pearly luster. ## Popular Localities The localities in the USA, Franklin and Sterling Hill, are considered classic and provide the best specimens in the world. Specimens from these places serve as a benchmark for this mineral. High-quality material also comes from Broken Hill in Australia, known for its large and well-formed crystals.

Care and storage

## Cleaning Specimens should be cleaned gently, using a soft brush and distilled water. Due to its perfect cleavage, ultrasonic cleaners and strong jets of water should be avoided, as they could lead to crystal delamination. ## What to avoid The mineral is sensitive to strong acids. Avoid sudden temperature changes and heating, which can lead to damage. Protect from impacts and falls, which can easily damage brittle crystals along cleavage planes. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratching by harder minerals. They should be protected from dust and direct, prolonged sunlight, although the mineral is not particularly light-sensitive.

Sources

IMA Mineral List (CNMNC)