The Mineral URANOCIRCITE
(under longwave UV light)
The structure of uranocircite is composed of phosphate tetrahedrons linked to uranium-oxygen groups that form distorted octahedrons. The phosphates and uranium groups lie in sheets that are weakly held together by water molecules. This structure produces the platy habit, the one perfect direction of cleavage, and the relative softness.
Uranocircite can lose water and convert to a different mineral called meta-uranocircite of the meta-autunite/meta-torbernite group of minerals. The change to meta-uranocircite will often produce a pseudomorph. A pseudomorph is generally an atom by atom replacement of one mineral's chemistry to form another mineral. The process leaves the crystal shape of the lost mineral intact. Pseudomorph means false (psuedo) shape (morph). In this case, the conversion is not so dramatic since it involves only the loss of a few water molecules, and therefore a good pseudomorph is likely to form. The conversion is irreversible and ongoing, and all collection specimens of a certain age are almost certainly at least partially converted.
Fine specimens should be stored in a closed container to avoid water loss. Remember, this is a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should be limited.
PHYSICAL CHARACTERISTICS:
- Colors are various shades of yellow to light yellow-green.
- Luster is vitreous to pearly on the main pinacoid.
- Transparency crystals can be transparent to translucent.
- Crystal System is tetragonal; 4/m 2/m 2/m
- Crystal Habits include platy square crystals usually in bladed aggregates. Crystals can form in parallel growths giving a "deck of cards" kind of look. Also as crusts, micaceous, foliated and scaly aggregates. Sometimes in attractive rosettes.
- Cleavage is perfect in one direction.
- Fracture is uneven.
- Hardness is 2.5
- Specific Gravity is approximately 3.5+ (above average for translucent minerals)
- Streak is a yellow tint.
- Associated Minerals are autunite, uranophane, torbernite, meta-torbernite, uraninite and other uranium minerals.
- Other Characteristics: radioactive, fluorescent green and cleavage sheets are slightly bendable.
- Notable Occurrences include Bergen, Germany; Autun, France; Cornwall, England; Mitchell Co., North Carolina and Mt. Spokane, Washington, USA; Zaire; Portugal and France.
- Best Field Indicators are color, crystal habit, fluorescence, radioactivity, associations and density.
 Amethyst Galleries' Mineral Gallery MINERALS |
URANOCIRCITE specimen urc-1
$ 55.00
$ 55.00
Dims: 1" x 3/4" x 3/8"
Wt: 2.3 g
Virgem de Lapa area, Minas Gerais, Brazil
I personally wouldn't be able to tell this specimen apart from the nearest autunite, but I haven't seen many uranium minerals before working on this site. The crystals are, of course, bright yellow, tabular, and surprisingly opaque for their thinness. The piece seems to be made up almost entirely of the mineral, though there are some suspiciously botryoidal, black formations that remind me of goethite. The uranocircite crystals are quite small, measuring just over 1/16 inch in diameter. I love the colors of uranium minerals like this; the yellow simply looks too bright to be a natural occurrence!
urc-1 ($ 55.00)
Virgem de Lapa area, Minas Gerais, Brazil
URANOCIRCITE specimen urc-2
$ 40.00
$ 40.00
Dims: 3.7 x 2.0 x 0.9" (9.4 x 5.1 x 2.3 cm)
Wt: 4.38 oz. (124.2 g)
Vogtland, Sachsen, Germany
This small hand specimen consists of a few flattened clusters of warped Uranocircite tablets. Every cluster shows some evidence of damage, but all tend to be rather flat, anyway, and likely formed in a narrow crevice. Their tetragonal form is all but undefinable, though some form is noticeable. All have the standard bright yellow coloration and pearly, micaceous luster of this mineral, and are opaque. The host rock on which they rest appears to be a very finely-grained granite.
urc-2 ($ 40.00)
Vogtland, Sachsen, Germany
URANOCIRCITE specimen urc-3
$ 65.00
$ 65.00
Dims: 4.7 x 4.3 x 1.6" (11.9 x 10.9 x 4.1 cm)
Wt: 1 lb., 5.2 oz. (602 g)
Vogtland, Sachsen, Germany
Many flattened Uranocircite blades are intergrown in scattered clusters on the granitic host rock of this piece. Individual blades are difficult to discern, and none appear to be complete and integral, most likely because they formed in a narrow crevice. Their form, likewise, is definable, but not very good. All have the bright yellow coloration and near-opacity that are standard for this mineral, and show a pearly luster. I cannot be sure that the host rock is made of granite, but it is definitely metamorphic in nature.
urc-3 ($ 65.00)
Vogtland, Sachsen, Germany
URANOCIRCITE specimen urc-4
$ 80.00
$ 80.00
Dims: 3.7 x 3.2 x 1.9" (9.4 x 8.1 x 4.8 cm)
Wt: 1 lb., 2.2 oz. (518 g)
Vogtland, Sachsen, Germany
This hand specimen consists of granular, possibly granitic base rock on which rest several flattened clusters of tabular Uranocircite crystals. These clusters appear to be in very good condition, as fresh damage is minimal. They are probably flattened because they formed in a narrow crevice between their base and another rock. The crystals are somewhat warped due to their intergrowth and the lack of space, but many have a surprisingly good tetragonal tabular form, with sharp edges and clean faces that possess a pearly luster. All have the standard bright-yellow coloration of Uranocircite, and a few of the more exposed blades are so thin that they are dimly transparent! There is a black discoloration on portions of the base rock, parts of which have a definitely dendritic shape.
urc-4 ($ 80.00)
Vogtland, Sachsen, Germany
URANOCIRCITE specimen urc-5
$ 60.00
$ 60.00
Dims: 5.4 x 3.4 x 1.6" (13.7 x 8.6 x 4.1 cm)
Wt: 1 lb., 2.7 oz. (529 g)
Vogtland, Sachsen, Germany
Scores of tiny, flattened Uranocircite blades coat a portion of the granular host rock of this large hand specimen. The blades do not exceed 0.2" (5 mm) in diameter and are flattened and heavily intergrown, so it is very difficult to assess any damage. They have a crystalline form, but it is all but destroyed by their intense intergrowth and lack of growing space. They do have the bright yellow coloration and pearly luster that are standard for this mineral, however. The host rock appears to be metamorphic in origin- I would guess that it is a finely-grained granite from its appearance.
urc-5 ($ 60.00)
Vogtland, Sachsen, Germany
URANOCIRCITE specimen urc-6
$ 40.00
$ 40.00
Dims: 3.5 x 2.9 x 1.2" (8.9 x 7.4 x 3.0 cm)
Wt: 7.69 oz. (218 g)
Vogtland, Sachsen, Germany
A loose cluster of many tiny Uranocircite blades rests on the granitic base of this hand specimen. These blades do not exceed 0.1" (3 mm) in diameter and are generally in good condition, though some damage is visible. All have good tetragonal tabular form and the standard bright yellow color and pearly luster. When placed under ultraviolet light, they glow a bright green.
urc-6 ($ 40.00)
Vogtland, Sachsen, Germany