Marrite: Properties and Occurrences

Marrite is depicted by the chemical formula PbAgAsS3. It is a monoclinic-prismatic mineral containing arsenic, lead, silver, and sulfur. It is the arsenic equivalent of mineral freieslebenite (PbAgSbS3) but also displays close polyhedral characteristics with sicherite and diaphorite. Marrite was named in honor of geologist John Edward Marr (1857–1933) of Cambridge, England.

Marrite is part of the monoclinic crystal class and 2⁄m point group. It is a mineral that occurs as a well-characterized substance of unknown composition in minute equant monoclinic crystals in the dolomite at Lengenbach, Valais, Switzerland.

General Information

  • Category: Sulfosalt mineral
  • Formula: (repeating unit) PbAgAsS3
  • Crystal system: Monoclinic
  • Crystal class: Prismatic (2/m) (same H-M symbol)
  • Color: Lead Gray, steel gray.

Properties

Under a microscope, marrite has a distinct anisotropic refractive index, meaning the velocity of light varies depending on the direction being traveled through the mineral. Crystal habit includes striated, meaning it forms parallel lines along with crystal faces; or tabular, meaning that structure dimensions are thin in 1 direction. When viewing the indicatrix of biaxial minerals, both optic axes are always perpendicular to one of the two circular sections.

  • Formula mass: 486.19 g/mol
  • Crystal habit: Tabular or striated crystals
  • Twinning: Partly bent twin lamellae observable in the polished section.
  • Cleavage: None
  • Fracture: Conchoidal
  • Tenacity: Brittle
  • Mohs scale hardness: 3
  • Luster: Metallic
  • Streak: Black with a brownish tint
  • Diaphaneity: Opaque
  • Specific gravity: 5.82
  • Optical properties: Biaxial

Occurrence

The only known occurrence of Marrite is the type locality of the Lengenbach quarry in Binntal, Valais, Switzerland. It is primarily formed because of hydrothermal activity, which involves water and high temperatures. Marrite is predominately found in dolomite along with a variety of other sulfosalts.

Association: Lengenbachite, rathite, tennantite, sartorite

 

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