Ichnusaite: Properties and Occurrences

Ichnusaite is a very rarely found mineral. Ichnusaite is a natural compound of thorium and molybdenum with the formula Th(MoO4)2·3H2O. It was discovered in Su Seinargiu, Sarroch, Cagliari, Sardegna, Italy in 2013.

This locality is also a place of discovery of the second natural thorium molybdate – nuragheite.

General Information

  • Category: Molybdate minerals
  • Formula: Th(MoO4)23H2O
  • Crystal system: Monoclinic
  • Crystal class: Prismatic (2/m) (same H-M symbol)

Fig: Ichnusaite

Properties

  • Color: Colorless
  • Cleavage: {100}, perfect
  • Tenacity: Brittle
  • Luster: Pearly adamantine

Occurrence

Muscovite, nuragheite, and xenotime-(Y) are the associates of ichnusaite. It is a secondary mineral in vugs in hydrothermal veins cutting porphyritic granite.

Association: Nuragheite, muscovite, xenotime-(Y), quartz, molybdenite

Crystal structure

The main features of the crystal structure of ichnusaite are:

  • electroneutral Th(MoO4)2(H2O)2 (100) sheets
  • ThO7(H2O)2 and MoO4 polyhedra polymerize to give the above sheets
  • sheets are stacked along [100] and held by hydrogen bonds

 

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