Torbernite

Torbernite, whose name derives from the Swedish chemist Torbern Bergman (1735-1784), is a radioactive, hydrated green copper uranyl phosphate mineral, found in granites and other uranium-bearing deposits as a secondary mineral. Torbernite is isostructural with the related uranium mineral, autunite.

The chemical formula of torbernite is similar to that of autunite in which a Cu²⁺ cation replaces a Ca²⁺. The number of water hydration molecules can vary between 12 and 8, giving rise to the variety of metatorbernite when torbernite spontaneously dehydrates. Their respective chemical compositions are the following:

Torbernite

Metatorbernite

Torbernite's most common alternative names are copper uranite and cupro-uranite.

Uses

As a radioactive mineral, torbernite has some limited significance as a uranium ore. Its vibrant green color and well-developed distinctive crystals (size: mm to a few cm) make it a sought-after collector's mineral, as well. However, torbernite, like other hydrated minerals, can easily suffer from loss of water molecules. This loss of water from the mineral leads to an alteration of torbernite specimens into its pseudomorph, meta-torbernite. Some collector's websites assert that any torbernite specimen more than a few years old should be considered fully transitioned to meta-torbernite. However, it likely depends on the temperature and relative humidity of ambient air in which specimens are stored.