Carminite: Properties and Occurrences

Carminite (Formula- PbFe3+2(AsO4)2(OH)2) is an anhydrous arsenate mineral containing hydroxyl. It is a rare secondary mineral that is structurally related to palermoite (Li2SrAl4(PO4)4(OH)4). Sewardite (CaFe3+2(AsO4)2(OH)2) is an analog of carminite, with calcium in sewardite in place of the lead in carminite. Mawbyite is a dimorph (same formula, different structure) of carminite; mawbyite is monoclinic and carminite is orthorhombic. It has a molar mass of 639.87 g. It was discovered in 1850 and named for the characteristic carmine color.

General Information

  • Category: Arsenate minerals
  • Formula: [PbFe3+2(AsO4)2(OH)2]
  • Crystal system: Orthorhombic
  • Crystal class: Dipyramidal (mmm)

Properties

Carminite is fairly soft, with a Mohs hardness of 3.5, between that of calcite and fluorite. Because of the lead content it is heavy, with a specific gravity of 5.03 – 5.18, although specimens from Mapimi are less dense at 4.10. Cleavage is distinct in one direction parallel to the c axis. Carminite is not radioactive and no piezoelectric effect has been detected.

  • Formula mass: 639.87 g/mol
  • Colour: Carmine red
  • Crystal habit: Typically bladed crystals, also acicular crystals, in spherical or tufted aggregates and as fibrous or drusy masses
  • Cleavage: Distinct on {110}
  • Tenacity: Brittle (D, All)
  • Mohs scale hardness: 3.5
  • Lustre: Vitreous, pearly on cleavages
  • Streak: Reddish yellow
  • Diaphaneity: Translucent
  • Specific gravity: 5.03 – 5.18

Occurrence

Carminite is formed as an uncommon alteration product of arsenopyrite (FeAsS) in the oxidized zones of some lead-bearing deposits. Common associates are wulfenite, scorodite, plumbojarosite, mimetite, dussertite, cerussite, beudantite, bayldonite, arseniosiderite, and anglesite.

The type locality is the Louise Mine, Bürdenbach, Altenkirchen, Wied Iron Spar District, Westerwald, Rhineland-Palatinate, Germany where it is associated with beudantite. At the Hingston Down Consols mine in Cornwall, England, carminite occurs with scorodite, mimetite, and pharmacosiderite.

 

Information Source:

en.wikipedia.org