Mendipite: Properties and Occurrences

Mendipite is an orthorhombic-disphenoidal mineral containing chlorine, lead, and oxygen. It is a rare mineral that was named in 1939 for the locality where it is found, the Mendip Hills in Somerset, England. It is an oxyhalide of lead with formula Pb3Cl2O2. This mineral is rare and occurs at the type locality within nodules in manganese oxide ores.

General Information

  • Category: Halide mineral
  • Formula (repeating unit): Pb3Cl2O2
  • Crystal system: Orthorhombic
  • Crystal class: Dipyramidal (mmm)
  • Formula mass: 724.50 g/mol.

Physical properties

Mendipite is found in columnar or fibrous aggregates, often radiated but more rarely straight long fibers, and in cleavable masses. The cleavage is perfect on {110} and fair on {100} and {010}. Fracture is conchoidal to uneven and the mineral is soft, with hardness only ​2 1⁄2 to 3, a bit less than that of calcite. Mendipite is soluble in dilute nitric acid, HNO3. It is not radioactive.

  • Color: Colorless to white, brownish cream, grey, yellowish, pink, red, or blue.
  • Crystal habit: Columnar or fibrous aggregates, often radiated, and cleavable masses.
  • Cleavage: Perfect on {110}, fair on {100} and {010}
  • Fracture: Conchoidal to uneven
  • Mohs scale hardness: ​2 1⁄2 to 3
  • Luster: Pearly to silky on cleavages; resinous to adamantine on fractures.
  • Streak: White
  • Diaphaneity: Translucent, rarely transparent
  • Specific gravity: 7.24
  • Optical properties: Biaxial (+)

Occurrences – In nodules in manganese oxide ores (Somerset, England).

The type locality is Churchill, Mendip Hills, Somerset, England, and type material is conserved at the Royal Swedish Academy of Sciences, Stockholm, Sweden. Other localities include Australia, Germany, Greece, Sweden, the UK, and the US.

At the Eleura Mine near Cobar, New South Wales, Australia, oxygenated groundwater reacted with sulfide minerals during the Cenozoic, forming supergene sulfides, as well as the sulfate minerals beudantite, anglesite, and baryte, together with some mimetite and native silver. Other localities for Mendipite include other English localities, Germany, Sweden, Poland, Greece, and Australia, among a few others.

Mendipite is found in association with hydrocerussite, cerussite, malachite, pyromorphite, calcite, chloroxiphite, diaboleite, and parkinsonite.

 

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