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, B├╝rdenbach, 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