Dictionary: torbernite   (tôr'bər-nīt')

A green radioactive mineral that is a hydrous crystalline phosphate of uranium and copper.

[After Torbern Olof Bergman (1735–1784), Swedish chemist.]

Environment

A secondary mineral on seams in granite and pegmatites.

Usually in thin square plates, sometimes in small bipyramids. Also micaceous flakes with indefinite outlines.

Emerald- to yellow-green. Luster glistening on base, vitreous in prism directions; hardness soft, perhaps 2-2Ɖ; specific gravity 3.2-3.6; fracture not visible as a rule; cleavage perfect basal and good frontal pinacoidal. Fragile and brittle; transparent (when fresh and 12 H ₂ O) to translucent (when 8 H ₂ O, metatorbernite).

Hydrous copper uranium phosphate (56.6% UO ₃ , 7.9% CuO, 14.1% P ₂ O ₅ , 21.4% H ₂ O, but part of the water is likely to evaporate spontaneously; metatorbernite has 8% H ₂ O). In a collection, one can assume that all crystals are dehydrated and should probably be labeled metatorbernite for nitpicking accuracy. (Very fragile when desiccated; try not to touch.)

Fuses easily to a black sphere. Gives copper flame in acid solution, and a fluorescent bead with sodium fluoride.

Can be confused with some rare copper phosphates and arsenates, though none has the square outline characteristic of torbernite. Resembles others of its group (autunite), but torbernite is not fluorescent and the others are. Zeunerite, the arsenic equivalent, resembles it closely, but would give arsenic fumes on charcoal and is more often bipyramidal.

Appears to be a late mineral, and its most frequent appearance is in thin green micaceous plates and small square crystals very lightly attached to the matrix, coating fissures in pegmatites and granite joints. It has also been found in some ore veins associated with other uranium minerals. Large and remarkably stable, thin, concave crystals over 1 in. (3 cm) across were found at Gunnislake, near Calstock, Cornwall. Next in size are the large crystals from Mt. Painter, South Australia. It also occurred in Portugal at Trancoso, in the Bois Noir, France, and in Saxony and Bohemia. It constitutes an ore of uranium only at Shaba (Katanga) in Zaȹre, where it forms magnificent, giant specimen crusts and is associated with the world's most colorful and remarkable uranium mineral suite. In French, tobernite may be known as chalcolite.

U.S. occurrences are infrequent; the best are well-formed ƈ-蕀 in. (5-10mm) plates coating a gray quartz in a quarry at Little Switzerland, North Carolina. Scattered crystals are found at many localities, but it is far rarer than autunite (next). Small bipyramidal crystals have been found at the Kinkel Quarry in Bedford, New York.

This mineral, autunite, and other high-water hydrates of their like, tend to dry and crumble in collections. Caution : Washing old specimens will probably result in their total destruction. While colorful, they are really not very satisfactory subjects to collect. Since uranium is radioactive, excessive exposure to its rays and dust is not recommended, and such actions as blowing on and breathing in its dust are hardly wise.

Torbernite
General
Category	Mineral
Chemical formula	Cu(UO2)2(PO4)2 · 8-12H2O (hydrated copper uranyl phosphate)
Identification
Color	Green
Crystal habit	tabular crystals, encrusted
Crystal system	Tetragonal
Cleavage	[001] Perfect; [100] Distinct
Fracture	Brittle
Mohs Scale hardness	2 - 2.5
Luster	Vitreous; Pearly
Streak	Pale green
Specific gravity	3.2
Diaphaneity	Transparent to opaque
Other Characteristics	Radioactive

Torbernite, whose name derives from the Swedish chemist Tornbern Bergmann (1735-1784), is a radioactive, green phosphate mineral, found in granites and other uranium-bearing deposits as a secondary mineral. Torbernite is isostructural with a related uranium mineral, autunite, with torbernite's lack of fluorescence a notable difference.

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

Uses of torbernite

As a radioactive mineral, torbernite has some significance as an ore of uranium. Its rich color and distinctive crystals make it a sought after collectors mineral, as well. However, torbernite, like other hydrated minerals, suffers from loss of water molecules. This loss of water from the mineral leads to an alteration of all torbernite specimens into its pseudomorph, meta-torbernite. Some collector's sites assert than any torbernite specimen more than a few years old should be considered fully transitioned to meta-torbernite.

As torbernite is radioactive, collectors are urged to take proper precautions in the handling and storage of any specimens.

Associated minerals

Torbernite frequently occurs in conjunction with other uranium minerals, as well as host rock minerals. These associated minerals include:

• autunite, Ca(UO₂)₂(PO₄)₂ · 8-12H₂O
• uraninite, UO₂
• uranophane, Ca}}(UO₂)₂Si₂O₇ · 6H₂O
• uranocircite, Ba(UO₂)₂(PO₄)₂ · 8-12H₂O
• topaz, Al[(F,OH)₂|SiO₄]

Identification

The most obvious factor in identifying torbernite is its radioactivity. However, since it is frequently found in association with other radioactive minerals, this may not be useful in separating one uranium mineral from the rest. A next step would be to check color. Most uranium-bearing minerals are bright yellow or green. As torbernite is exclusively green, this can be a useful secondary fact. Crystal habit is also useful, but as it shares a similar structure and color with autunite, torbernite's lack of fluorescence can distinguish the two. Nonetheless, regardless of identification, it is likely that at least some of the specimen will have already altered to meta-torbernite.

See also

• List of minerals
• List of minerals named after people

External links

• Webmineral
• Mindat
• Mineral Galleries
• Mineralienatlas:Torbernit (WiKi)

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