Small but outstanding crystals of the very rare tellurites cliffordite (yellow) and mackayite (green) from the type locality: San Miguel Mine, Moctezuma, Sonora, Mexico. — Photo: David Hospital · CC BY-SA 4.0
Cliffordite
Cliffordite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula UTe⁴⁺₃O₉.
Key properties: Mohs hardness 4; specific gravity 6.57; Adamantine luster.
IMA symbol Cff, IMA status: approved, named in 1966.
Occurs as rare incrustations along fractures in the oxidized zone of hydrothermal Au–Ag telluride deposits.
It is found associated with Mackayite, barite, quartz, “limonite” (San Miguel prospect, Mexico); tellurium, paratellurite, quartz (Moctezuma mine, Mexico).
The mineral was named to honor Professor Clifford Frondel (1907–2002), Harvard University, Cambridge, Massachusetts, USA, for his contributions to uranium mineralogy.