Arsenmarcobaldiite

Chemical formula: Pb₂+₁₂(As₃+₃.₂Sb₃+₂.₈)S₂-₂₁

Arsenmarcobaldiite is a rare sulfosalt mineral of lead, arsenic, and antimony, occurring as metallic, tabular crystals.

## Characteristics Arsenmarcobaldiite is a mineral from the sulfosalt group, chemically classified as a sulfosalt of lead, arsenic, and antimony. It forms thin, tabular crystals with a hexagonal outline, reaching up to 200 micrometers in size. It occurs as inclusions in other minerals, mainly sartoryte. Its appearance is typical for many sulfosalts – it has a metallic luster and a dark gray to black color. ## Physical Properties Due to the small size of the crystals, most physical properties have not been precisely determined. The mineral is opaque and has a metallic luster. Its hardness and density have not been measured, but they can be estimated as typical for lead sulfosalts – it is likely a relatively soft and very dense mineral. ## History and Name The mineral's name refers to its chemical composition (dominance of arsenic over antimony) and its relation to marcobaldiite, another mineral from the same group. It was formally described by a research team led by L. Bindi and approved by the International Mineralogical Association (IMA) in 2016 under number 2016-031. The discovery was made on samples from the Lengenbach quarry in the Binn Valley (Binntal) in Switzerland.

Properties

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

Diagnostic features

## Identification Identification of arsenmarcobaldiite is impossible without advanced laboratory techniques. Due to its occurrence as microscopic inclusions, it requires analysis using an electron microscope (EDS/WDS) to confirm its chemical composition and X-ray diffraction to determine its crystal structure. ## Distinguishing from Similar Minerals It can be confused with many other sulfosalts from the Lengenbach quarry, such as sartoryte, dufrénoysite, rathite, or marcobaldiite. Differentiation relies solely on precise chemical analysis, which reveals the specific ratio of lead, arsenic, and antimony. ## Crystal Forms The mineral forms very small, thin, tabular crystals with a hexagonal outline. They usually occur as single inclusions within other minerals.

Geological environment

## Genesis Arsenmarcobaldiite forms as a result of hydrothermal processes in metal deposits. In its type locality (Lengenbach quarry), it is associated with dolomitic marbles (carbonate rocks) that have undergone metamorphism and metasomatism. It crystallizes from solutions rich in sulfur, lead, arsenic, and antimony. ## Mineral Associations This mineral occurs in paragenesis with other sulfosalts. It is most commonly found as inclusions in sartoryte. It also co-occurs with dufrénoysite, rathite, baumhauerite, jordanite, and realgar. ## Localities The only confirmed locality of arsenmarcobaldiite in the world is its type locality: the Lengenbach quarry in the Binn Valley (Binntal), Valais canton, Switzerland. This is a site known for the occurrence of many rare and unique sulfosalts.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, arsenmarcobaldiite is not evaluated according to typical criteria such as size or color. The collector's value of a specimen lies in the confirmed presence of this mineral on the matrix (usually on sartoryte) and its origin from the type locality. The most valuable samples are those whose composition has been analytically verified.

Care and storage

## Cleaning Specimens containing arsenmarcobaldiite, usually as inclusions in other minerals, should be cleaned with utmost care. The safest method is to use compressed air to remove dust. Any contact with water or chemicals is inadvisable. ## What to Avoid Avoid contact with water, acids, and any chemical agents that may react with sulfides and cause their oxidation or decomposition. The mineral is potentially sensitive to changes in temperature and humidity. As a mineral containing arsenic and lead, avoid inhaling dust and wash hands after any contact. ## Storage Specimens should be stored under stable conditions, in a dry place, away from direct sunlight. It is best to place them in closed, padded collector's boxes or display cases to minimize the risk of mechanical damage and oxidation.

Sources

IMA Mineral List (CNMNC)