Matlockite: Properties and Occurrences

Matlockite a mineral (PbFCl) consisting of lead chloride and fluoride. It is a rare lead halide mineral, named after the town of Matlock in Derbyshire, England, where it was first discovered in a nearby mine. It is a tetragonal-ditetragonal dipyramidal mineral containing chlorine, fluorine, and lead. Matlockite (chemical formula: PbFCl) gives its name to the matlockite group which consists of rare minerals of a similar structure.

General Information

  • Category: Halide minerals
  • Formula: (repeating unit) PbFCl
  • Crystal system: Tetragonal
  • Crystal class: Ditetragonal dipyramidal (4/mmm)
  • Colour: Colourless to yellow and greenish.

Properties

It is a light, translucent creamy-yellow color, but heavy in weight having a density that is over 7.1. It is a tetragonal fluoride and chloride of lead, usually occurring as transparent, colorless to yellow or yellowish-brown tabular crystals.

  • Crystal habit: Flattened, tabular crystals occurring as aggregates, rosettelike, radiating, hemispherical; also massive
  • Cleavage: {001}, perfect
  • Fracture: Uneven to subconchoidal
  • Tenacity: Brittle
  • Mohs scale hardness: 2.5 – 3
  • Luster: Adamantine, pearly on {001}
  • Diaphaneity: Transparent
  • Specific gravity: 7.1 – 7.2
  • Optical properties: Uniaxial (-)

Occurrences – In the oxide zone of some lead-bearing mineral deposits.

The mineral, a lead fluorochloride (formula PbFCl), was discovered sometime around the early 1800s at Bage Mine at Bolehill near Matlock, together with specimens of phosgenite and anglesite. Although phosgenite was known at this time, it seems likely that matlockite itself remained unappreciated as a new mineral for some fifty years. It was given the name by Greg in 1851.

A very large specimen 10 cm across, and originating from Derbyshire, exists in the collections of the American Museum of Natural History. A 7 cm specimen can be found in the collection of Derby Museum and Art Gallery.

Association: Matlockite has been reported from a variety of locations since its discovery at the type locality of Derbyshire. The mineral is also found in Tiger, Arizona, Laurium in Greece, a mine near Essen in Germany, and near Campiglia in Tuscany.

 

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