Dewitite

Chemical formula: Ag₁+zTl₁+₁₀-x-zPb₂+₂xSb₃+₄₂-x-yAs₃+yS₂-₆₈ (₀.₀₉ ≤ x ≤ ₂.₁₃, ₁₃.₉₉ ≤ y ≤ ₁₉.₇₉, ₀.₁₀ ≤ z ≤ ₀.₅₀)

Dewitite is a rare, lead-gray sulfosalt with a metallic luster, occurring as tiny, acicular crystals.

## Characteristics Dewitite is a complex sulfosalt containing thallium, lead, antimony, arsenic, and silver. It forms very tiny, needle-like or acicular crystals, which usually occur as tangled aggregates or coatings. Its color is lead-gray, and on a fresh surface, it exhibits a strong, metallic luster. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties This mineral is opaque and has a metallic luster. Its hardness and density have not been precisely measured due to the very small size and rarity of samples. It is brittle, and its crystals are easily damaged. ## Colors and Varieties Dewitite occurs in a uniform, lead-gray color. No color varieties or commercial varieties are known. ## History and Name The mineral's name honors Prof. Dr. Hessel de Wit (born 1951), emeritus professor of structural geology at Utrecht University in the Netherlands, in recognition of his contributions to geological research. The mineral was approved by the International Mineralogical Association (IMA) in 2017, and its description was published in 2019. The type locality is the Lengenbach quarry in the Binn Valley, Switzerland. ## Applications Dewitite has no industrial applications. It is solely an object of scientific and collecting interest, sought after by specialists collecting sulfosalt minerals or specimens from the type locality.

Properties

Luster: Metallic
Streak: Black
Transparency: Opaque
Crystal system: Triclinic

Diagnostic features

## Identification Identification of dewitite is possible almost exclusively using advanced laboratory methods, such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD). Visually, it is indistinguishable from many other fine-grained, gray sulfosalts. It occurs as very small, needle-like crystals with a metallic luster. ## Differentiation from Similar Minerals Dewitite can be confused with numerous other thallium, lead, and arsenic sulfosalts found in Lengenbach, such as hutchinsonite, wallisite, imhofite, or rathite. Definitive differentiation requires specialized chemical and structural analysis. ## Crystal Forms Dewitite crystals are very small, elongated, and acicular, often with a nearly square cross-section. They usually form chaotic, tangled aggregates or radial clusters intergrown with other minerals, mainly dolomite.

Geological environment

## Genesis Dewitite forms as a result of hydrothermal processes in polymetallic deposits. In its type locality (Lengenbach quarry), it crystallizes in fissures and small cavities within dolomitic metamorphic rocks (dolomitic marbles) that have been subjected to solutions rich in sulfur, arsenic, thallium, lead, and other metals. ## Mineral Associations This mineral co-occurs with other rare sulfosalts, such as hutchinsonite, rathite, sartorite, as well as realgar, orpiment, and pyrite. It is most commonly found in association with dolomite, which constitutes the host rock. ## Localities The only confirmed locality of dewitite in the world is the Lengenbach quarry in the Binn Valley, Valais Canton, Switzerland. This is a classic and world-renowned locality for rare thallium and arsenic sulfosalts.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of dewitite specimens is primarily assessed based on the abundance and visibility of its crystals within the host rock (matrix). Since the crystals are microscopic, samples where dewitite aggregates form distinct, dense clusters are most valued. Association with other well-formed, rare minerals from this locality is also important. ## Popular Localities The only source of specimens is the Lengenbach quarry in Switzerland. Material from this locality is highly prized by collectors specializing in systematic minerals and rare sulfosalts.

Care and storage

## Cleaning Dewitite specimens are extremely delicate and susceptible to oxidation. Mechanical cleaning is not recommended. If necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Absolutely avoid contact with water, acids, cleaning agents, and other chemicals. The mineral is sensitive to changes in humidity and temperature. Prolonged exposure to light and air can cause slow oxidation and dulling. ## Storage It is recommended to store specimens in sealed, acid-free "micromount" boxes, away from light, moisture, and chemical contaminants. The best environment is a stable atmosphere with low humidity.

Sources

IMA Mineral List (CNMNC)