Manganoquadratite

Chemical formula: Ag₁+Mn₂+As₃+S₂-₃

A very rare silver, manganese, and arsenic sulfosalt, forming tiny, metallic-lustered crystals in paragenesis with other rare minerals.

## Characteristics Manganoquadratite is a sulfosalt of complex chemical composition, containing silver, manganese, arsenic, and sulfur. It is the manganese analogue of quadratite. It occurs as very small, thin, tabular crystals, rarely exceeding fractions of a millimeter in size. The crystals have a square or rectangular outline, which refers to its tetragonal symmetry. It is an opaque mineral with a strong, metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and black color. Its density, calculated based on chemical composition and unit cell parameters, is approximately 5.05 g/cm³. Hardness has not been precisely determined due to the small size of the crystals, but like most sulfosalts, it is a relatively soft mineral. ## Colors and Varieties It is usually black or dark gray. Due to its extreme rarity, no color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1995 by T. B. Williams, A. Pring, and A. C. Roberts. Its name refers to the dominant manganese (Latin: *manganum*) in its composition and its structural and chemical similarity to quadratite. The name quadratite, in turn, comes from the Latin word *quadratus* (square), referring to the habit of its crystals. The type locality is the Lengenbach quarry in the Binn Valley (Binntal) in Switzerland. ## Applications Due to its extreme rarity and microscopic size, manganoquadratite has no practical application. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Luster: Metallic
Streak: Black
Density: 5.05
Cleavage: Perfect on {001}
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of manganoquadratite is impossible without advanced analytical techniques. Due to its microscopic size, identification relies on chemical analysis (EDS/WDS) to confirm the presence of silver, manganese, arsenic, and sulfur. A preliminary indication may be the tetragonal crystal form and co-occurrence with other rare sulfosalts from Lengenbach. ## Distinguishing from Similar Minerals Manganoquadratite can be confused with many other black, metallic sulfosalts found in the same locality, especially its cadmium analogue – quadratite. Differentiation from quadratite, trechmannite, hatchite, or sinnerite requires specialized chemical analysis. ## Crystal Forms It forms very small, thin, tabular crystals with a square or rectangular outline. They usually occur as single, isolated crystals grown on a substrate, most often dolomite.

Geological environment

## Genesis Manganoquadratite forms as a result of low-temperature hydrothermal processes. It is a product of crystallization from solutions rich in arsenic, sulfur, silver, and manganese. It occurs in veins cutting saccharoidal dolomites. ## Mineral Associations This mineral occurs in association with other rare arsenic sulfosalts. Its most common associations include quadratite, realgar, orpiment, trechmannite, hatchite, wallisite, and smithite. These minerals most often grow on a dolomite matrix. ## Localities The only confirmed locality for manganoquadratite in the world is the Lengenbach quarry in the Binn Valley (Binntal), Valais canton, Switzerland. This is the classic and type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of manganoquadratite specimens, being a micromineral, is assessed based on several criteria. The sharpness and development of the crystals are most important – the better defined and undamaged, the more valuable. Size, even if measured in fractions of a millimeter, is significant. Specimens where manganoquadratite co-occurs with other rare and well-formed minerals, creating an aesthetic composition, are highly prized. ## Popular Localities All known and valued manganoquadratite specimens by collectors come from a single location in the world – the Lengenbach quarry in Switzerland. This is the only locality from which this mineral has been obtained.

Care and storage

## Cleaning Manganoquadratite specimens are typically microminerals and are very delicate. Cleaning should be kept to an absolute minimum. For dust removal, it is best to use a photographic air blower or a stream of compressed air from a safe distance. Any contact with water and chemical agents should be avoided. ## What to Avoid Manganoquadratite, as a sulfosalt, is sensitive to moisture and atmospheric oxygen, which can lead to its oxidation and tarnishing. Avoid contact with all liquids, acids, and detergents. Ultrasonic cleaners must not be used. The mineral is soft and susceptible to scratching. ## Storage It is recommended to store specimens in sealed, airtight "micromount" boxes, which protect against dust, moisture, and mechanical damage. Store in stable conditions, away from direct sunlight and heat sources.

Sources

IMA Mineral List (CNMNC)