Quadratite

Chemical formula: Ag₁+Cd₂+As₃+S₂-₃

Quadratite is a rare silver, cadmium, and arsenic sulfosalt, forming characteristic, tabular crystals with a metallic luster.

## Characteristics Quadratite is a very rare mineral from the sulfosalt group, chemically a complex sulfide of silver, cadmium, and arsenic. Its name refers to its tetragonal crystal system and typical square crystal habit. It usually forms very small, thin, tabular crystals, rarely exceeding 1 mm. It occurs as single crystals or small aggregates on a rock matrix. It is opaque and has a black color with a metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. Its Mohs hardness is approximately 3, and its density is quite high at 5.12 g/cm³. The crystals exhibit perfect cleavage in one direction. ## Colors and Varieties Quadratite is a mineral with a constant composition and a uniform, black color. No color or commercial varieties are distinguished. ## History and Name Quadratite was discovered in the Lengenbach quarry in the Binn Valley (Binntal) in Switzerland, a location known for its unique sulfosalts. It was first described in 1973 by S. Graeser. The name "quadratite" comes from the Latin word *quadratus* meaning "square", which is a direct reference to its tetragonal crystal system and the typical appearance of its crystals. ## Uses Due to its extreme rarity and microscopic size, quadratite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections specializing in mineral systematics or minerals from Lengenbach-type localities.

Properties

Mohs hardness: 3
Luster: Metallic
Streak: Black
Density: 5.12
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Quadratite is identified by its unique appearance – small, black, tabular crystals with a square outline and metallic luster. Key to identification is its locality (Lengenbach quarry) and its association with other rare sulfosalts. Confirmation requires advanced analytical methods, such as EDS analysis. ## Distinguishing from Similar Minerals It can be confused with other rare, black sulfosalts from Lengenbach, such as hatchite or wallisite. Distinguishing it based on visual characteristics is practically impossible without specialized equipment. The characteristic square crystal habit is the best visual clue. ## Crystal Forms Quadratite crystallizes in the tetragonal system. It forms thin, tabular crystals with a square or rectangular outline. Crystals are usually very small, reaching sizes below one millimeter.

Geological environment

## Genesis Quadratite forms as a result of hydrothermal processes in dolomitic deposits. Its formation is linked to metamorphism, which released metals and sulfur from the surrounding rocks, leading to the crystallization of rare sulfosalts in rock fractures and cavities. ## Mineral Associations This mineral occurs in association with other rare sulfosalts of arsenic, lead, and thallium, typical of the Lengenbach locality. It most commonly co-occurs with realgar, orpiment, sartorite, hatchite, and dolomite. ## Localities The only confirmed occurrence of quadratite in the world is the Lengenbach quarry in the Binn Valley (Binntal), in the canton of Valais, Switzerland. This is its type locality and currently the only known one.

Rarity

Extremely rare

For collectors

## Quality Criteria The most important criterion for evaluating a quadratite specimen is the quality and development of its crystals. Specimens with sharp, well-defined crystals with a clearly square outline are sought after. Rich aggregates of crystals on a rock matrix and associations with other rare minerals from this locality are also highly valued. The size of the crystals, even if exceeding 0.5 mm, significantly increases the value of the specimen. ## Popular Localities The only source of quadratite specimens is the Lengenbach quarry in Switzerland. Material from this locality is extremely prized by collectors specializing in rare minerals and systematics.

Care and storage

## Cleaning Quadratite specimens are extremely delicate and small, so mechanical cleaning should be avoided. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid The mineral is sensitive to chemicals, especially acids, which can damage it. It should be protected from moisture, sudden temperature changes, and direct, strong light. Due to its low hardness, it is very susceptible to scratches and mechanical damage. ## Storage Quadratite specimens should be stored under stable conditions, preferably in sealed "micromount" containers, which protect them from dust, moisture, and physical damage. Display should be away from heat sources and direct sunlight.

Sources

IMA Mineral List (CNMNC)