Metatorbernite

Metatorbernite
Green platy crystals on granite. Specimen from Redruth, Cornwall, UK
General
Category	Phosphate minerals
Formula (repeating unit)	Cu(UO2)2(PO4)2·8(H2O)
Strunz classification	08.EB.10
Identification
Color	Light to dark green
Crystal habit	Flat plates
Crystal system	Tetragonal-dipyramidal
Cleavage	Perfect
Fracture	Brittle
Mohs scale hardness	2.5
Luster	Vitreous, adamantine
Streak	Light green
Specific gravity	3.7-3.8
Refractive index	1.624-1.626
Other characteristics	Radioactive

Metatorbernite (or meta-torbernite) is a radioactive phosphate mineral, and is a dehydration pseudomorph of torbernite. Chemically, it is a copper uranyl phosphate and usually occurs in the form of green platy deposits. It can form by direct deposition from a supersaturated solution, which produces true crystalline metatorbernite, with a dark green colour, translucent diaphaneity, and vitreous lustre. However, more commonly, it is formed by the dehydration of torbernite, which causes internal stress and breakage within the crystal lattice, resulting in crystals composed of microscopic powder held together using electrostatic force, and having a lighter green colour, opaque diaphaneity, and a relatively dull lustre. As with torbernite, it is named after the Swedish chemist Tornbern Bergmann. It is especially closely associated with torbernite, but is also found amongside autunite, meta-autunite and uraninite.

References

• MinDAT
• Webmineral
• Uranium minerals

Metatorbernite from the Margabal Mine, Entraygues-sur-Truyère, France. Size: 4 x 3 x 1.8 cm.