• Chemistry: UTe3O9, Uranium Tellurite
  • Class: Sulfates
  • Subclass: Tellurates
  • Uses: Only as mineral specimens.
  • Specimens

Cliffordite is named after mineralogist Clifford Frondel who also has given his name to the phosphate mineral frondelite.

Cliffordite is a very rare tellurium mineral. The type locality for cliffordite, the San Miguel Mine and other mines of Moctezuma, Sonora, Mexico, is famous for rare tellurium minerals.

The symmetry of cliffordite is the unusual bar 3 2/m of the Diploidal Class. A class of symmetry that contains the sulfide mineral pyrite, among others. Cliffordite is a radioactive mineral and should be stored away from minerals that are affected by radioactivity and of course human exposure should be limited.


  • Color is bright yellow to sulfur yellow.
  • Luster is adamantine.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; bar 3 2/m.
  • Crystal Habits include small octahedral crystals.
  • Hardness is 4.
  • Specific Gravity is approximately 6.6 - 6.7 (very heavy for translucent minerals).
  • Streak is bright yellow.
  • Other Characteristics: Specimens are slightly radioactive.
  • Associated Minerals include tellurium and other tellurates and tellurites.
  • Notable Occurrences are limited to the type locality of San Miguel Mine, Moctezuma, Sonora, Mexico.
  • Best Field Indicators are locality, softness, high density, luster, radioactivity and cleavage.
Popular Members of the Sulfates Class


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