Corkite: Properties and Occurrences

Corkite is a phosphate mineral in the beudantite subgroup of the alunite group. It is a phosphate-sulfate-hydroxide of lead and iron [formula- PbFe[(OH)6:SO4:PO4] that is isomorphous with beudantite. It is A trigonal-ditrigonal pyramidal mineral containing hydrogen, iron, lead, oxygen, phosphorus, and sulfur.

Corkite is named after County Cork, Ireland; the location where the first notable amount was discovered in 1869. Like many of the other minerals in the beudantite group, corkite is a relatively uncommon, secondary mineral that occurs in oxidation zones near hydrothermal base metal deposits.

General Information

  • Category: Phosphate minerals
  • Formula: PbFe[(OH)6:SO4:PO4]
  • Crystal system: Trigonal
  • Crystal class: Ditrigonal pyramidal (3/m) (same H-M symbol)

Properties

It is the phosphate analogue of beudantite and with it, a complete solid solution range exists. Corkite will also form a solid solution with kintoreite.

  • Formula mass: 667.82 g/mol
  • Color: Brown to light yellowish brown, pale yellow, yellowish green to dark green
  • Crystal habit: Crystals pseudocubic rhombohedral with prominent {1011}.
  • Mohs scale hardness: 3.5 – 4.5
  • Luster: Vitreous, resinous
  • Diaphaneity: transparent
  • Specific gravity: 4.295 (measured), 4.31 (calculated)

Occurrence: A rare secondary mineral formed at low temperatures or by weathering in oxidized hydrothermal base-metal deposits.

Association: It occurs associated with pyromorphite, malachite, plumbojarosite, limonite and quartz.

 

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