Metatorbernite

 IMA-GP
Uranium 40.2a.13.2
(Dana Classification Number)
(Images) 7/E.02-60
(Strunz ID)

    (see Notes concerning directly formed Metatorbernite    
  and That which is the pseudomorph after Torbernite  

Property Data Remarks
Named for: Being the meta- form of Torbernite, which is named for Torber Bergmann (1735-1784), Swedish chemist
Alternate
    Name(s):
  		•  
    Mineral Class:
    Phosphates, Arsenates and Vanadates
      Uranylphosphates and Uranylvanadates with
    [UO2]2+ - [PO4 | AsO4]3- and
    [UO2]2+ - [V2O8]6-
        Meta-Autunite group
    		 
    Chemical
        Formula:    		 Cu(UO2)2(PO4)2 · 8-12(H2O)  
    Chemical
        Composition:
    Copper: (Cu) 6.78%
    Hydrogen: (H) 1.72%
    Oxygen: (O) 34.13%
    Phosphorus: (P) 6.61%
    Uranium: (U) 50.77%
    		by weight
    Molecular
        Weight:    		 937.67 daltons (amu)
    Specific
        Radioactivity:

    (All radiation is for a 1 gram, fully aged specimen)

    Specific Activity Dose Rate
    Becquerels Curies milliRems/hour microSieverts/hour
    9.0879 × 1005 2.46 × 10-06 1.27 12.7

    Estimated Average Annual Exposure: 360 mRem (3.6 milliSieverts)
    Crystalography:
    System: Tetragonal - Dipyramidal
    Axial Ratios: a: 1
    c: 2.48328
    Cell Dimensions: a: 6.969 Å
    c: 17.306 Å
    Z: 2
    V: 840.50 Å3
    DenCalc: 3.70
    H-M Symbol: 4/m
    Space Group: P4/n
    X-Ray Diffraction:
      By Intensity ( I/Io )    		 (1): 3.68 Å
    (1): 8.71 Å
    (0.8): 3.48 Å
    		Metatorbernite
    Crystals
    Habit:
  • Flat plates
  • A dehydration pseudomorph after Torbernite
    		•   
    Cleavage:
    [001] Perfect
    [010]  
    [100]  
    		 
    Fracture: Very brittle  
    Moh's
        Hardness:    		 2.5  
    Density: 3.7 - 3.8 grams/cm3
    Color: Pale to Dark green to almost Black  
    Streak: Pale green to light green  
    Luster: Vitreous - Adamantine - Dull  
    Diaphaneity: Transparent to Translucent to Opaque  
    Pleochroism:
    (x):  
    (y:)  
    (z:)  
    		 
    Ultra Violet
        Fluorescence:

    Non-Fluorescent

    (The lack of fluorescence best distinguishes this mineral from Autunite)

    		  
    Magnetism: Non-magnetic  
    Occurance:
  • May be formed directly in hydrothemal deposits from saturated or super-saturated solutions (a-Metatorbernite)
  • Often found as a dehydration pseudomorph after Torbernite, a secondary mineral formed from the alteration of Uraninite
    		•   
    Associated
        Minerals:

    Almandine, Arsenopyrite, Autunite, Azurite, Barite, Biotite, Bornite, Brochantite, Calcite, Cassiterite, Chalcocite, Chalcopyrite, Chrysocolla, Copper, Covellite, Fluorapatite, Fluorite, Galena, Goethite, Gypsum, Hematite, Malachite, Marcasite, Meta-Autunite, Microcline, Muscovite, Phosphuranylite, Pyrite, Quartz, Schorl, Siderite, Sphalerite, Torbernite, Uraninite, Uranophane, Zircon

    Mineral   -   > 54% of sites
    Mineral   -   > 36% of sites
    Mineral   -   > 18% of sites
    Minerals   -   Uranium & Thorium
    mineral links

    		These are minerals known to be found with Metatorbernite
    Localities:

    Relatively common

    (Metatorbernite localities)
    Notes:

    Strongly radioactive a- and b-particles, g-rays.

    Crystals are probably metamict.
     

    Observed Differences In Metatorbernite Crystals

    There are two possible ways that Metatorbernite can form: from direct deposition from a highly concentrated solution (which I have designated as a-Metatorbernite for discussion purposes only); and from Torbernite losing water (designated as b-Metatorbernite also only for discussion purposes). Both are believed to have the same properties, and therefore to be the same mineral. They differ from each other only in their general appearence and method of formation. The greatest differences are that a-Metatorbernite is a dark green color, is transparent to translucent, and has a vitreous luster. b-Metatorbernite is a lighter green, often changing tone within the same pseudomorph crystal, opaque, and has a relatively dull, or earthy, luster.

    These differences are attributable to the b-Metatorbernite being formed by the dehydration of Torbernite, and it is therefore a pseudomorph of Torbernite, and not the true crystal form of Metatorbernite. When Torbernite loses water, there is ~16% shrinkage in its unit cell volume, which causes a large internal stress to develope within the crystal lattice. This stress causes the crystal to break up into a powder that cannot be discerned through a 60X microscope. The pseudomorph crystal seen is actually composed of many submicroscopic crystal fragments that can be described as a powder whose particles's crystaline latices are highly oriented to each other, and joined electrostatically into the the form of the original Torbernite crystal. This follows the more traditional view of the formation of Meta-forms of Uranyl minerals.

    The a-Metatorbernite is believed to be formed by the direct deposition of the mineral from a saturated, or supersaturated, solution, resulting directly in the dehydrated form of Torbernite, or Metatorbernite. This is analogous to the formation of Anhydrite in desert areas of the world. For this reason, its observed crystal form should be taken as the true shape of the Metatorbernite crystal as it occurs in nature.

    Again, the designations of a-Metatorbernite and b-Metatorbernite are strictly for conversational notation, and have no other reality or purpose. Their use beyond this web-site must be with this caution, as the desigantions are purely conversational and not scientific.

    My thanks to Dr. Andrew Locock, Curator of Mineralogy, Natural History, Royal Ontario Museum, Toronto, Ontario, Canada. His comments pointing out the structure of the Metatorbernite pseudomorph after Torbernite helped explain what I have been observing vthrough my microscope. Any errors in the above discussion are due to my misinterpretation of his explaination, and not his.

    Metatorbernite Images

    Specimen #1
    (001a) (001b) (001c) (001d)
      (intergrown w. Autunite
    (001e) (001f) (001g) (001h)
    (growing on Calcite matrix,
    w. Autunite)    		 (growing on Calcite & Uraninite matrix)

         		  
    (001i) (001j) (001ka) (001kb)
        (same 'Book' sheaf rotated 90°'s)
    (001m)
    (close-up view of the Autunite)
    Margabal, Eutrayques, Aveyron, France


    Specimen Notes

     

    Occurrence -  

     

    Crystal Form - This specimen is of the b-Metatorbernite form of this mineral.

     

      -  

     

    Physical Properties - Weight: 81.65 grams

     

    Specimen #2
      (Saléeite-003a) (Saléeite-003b)  
       
    (002a) (002b) (002c) (002d)

     
    Mashamba West Mine, Kolwezi, Shaba (Katanga), Congo (Zaïre)


    Specimen Notes

    This is an unusual specimen in that seven (7) uranium minerals have been identified on it, five(5) within 1 cm of the vug of primary interest. These minerals are: Cuprosklodowskite; Kasolite (?); Masuyite; Metatorbernite; Uraninite; and Uranophane. Some areas show hints of modification to Ianthinite as well. The Saléeite is the mineral of primary interest on this specimen.

    Occurrence - The specimen is primarily Uraninite and silicate rock. The Uraninite near the vug holding the Metatorbernite has a zone of modification to Uranophane. This can be seen in the upper corner of image Metatyuyamunite-002a, and in the images of the Uraninite (Uraninite Specimen #6) of this specimen.

    The presence of a-Metatorbernite indicates that the deposits are of hydrothermal genisis. As the location is hot, arid terrain, it is not known if the water was heated by solar or geothermal means.

    Crystal Form - This is a specimen of the a-Metatorbernite form of this mineral. In image 002a, the [013/103] facets can be seen on one crystal, and hinted at on the others. Usually, this facet is replaced by a more vertical 'step' at the [013/103] and [001] edge.

    The [110] facets do not appear on the Metatorbernite crystals of this specimen. Several crystals have a very slight rounding of their corners, which is the usual appearance of this facet.

    Note the free intergrowth of Cuprosklodowskite (image 002d) and Metatyuyamunite (image 002b) with the Metatyuyamunite. The growth of the crystals of these two minerals does not interfere noticably with the growth of the Metatorbernite crystals, nor does the Metatorbernite interfere greatly with theirs. It is not known if they grew simultaneously with the Metatorbernite, or if the Metatorbernite grew around them at a later time.

    Appearance - The luster of the Metatorbernite crystals is vitreous, the surfaces appearing to be almost polished. The diaphaneity is nearly transparent. The color is dark green.

    The overall appearance of these crystals is typical for a-Metatorbernite.

    Specimen #3
    (Schoepite-001a) (Schoepite-001b) (Schoepite-001c)
    Musonoi mine, Kolwezi, Shaba (Katanga), Congo (Zaïre)  


    Specimen Notes

    See notes on Schoepite Specimen #1.

    Crystal Form - This specimen shows the a-Metatorbernite form of this mineral. In image 001c, the [013/103] facets can be seen on one crystal, and hinted at on the others. Usually, this facet is replaced by a more vertical 'step' at the [013/103] and [001] edge.

    The [110] facet can be seen as a rounded corner on one of the Metatorbernite crystals located in the lower right corner of image Schoepite-001b and in the center of the right half of image Schoepite-001c (same crystal). The other Metatorbernite crystals do not have any rounding of their corners, which is the usual absence of this facet.

    Appearance - The luster of the Metatorbernite crystals is vitreous. The diaphaneity is nearly transparent. The color is dark green. The overall appearance of these crystals is typical for a-Metatorbernite.

    Specimen #4
    (004a) (004b) (004c) (004d)

     
    Musonoi Mine, Kolwezi, Shaba (Katanga), Congo (Zaïre)


    Specimen Notes

    The references below to 'under-side' is made only in regard to it being the area of contact with the host rock. There is no indication of in-ground orientation for the specimen.

    Occurrence - Only a small trace of the original matrix is visable on the underside of the specimen.

    Crystals - This is a highly unusual specimen of the a-Metatorbernite crystal form of this mineral. Usually, the crystals are solitary, or if in close proximity, just one or two touching. On this specimen, not only are they intergrown, much in the way that the b-Metatorbernite is, but in some places, smaller Metatorbernite crystals have begun growing on the larger ones. The smallest of these can be made out only as a druse on several of the larger crystals, with only a hint of their being square plates.

    The [011] crystal face is present on many of these crystals. The presence of this face is also highly unusual in that it is very well formed on most of its occurrances. This face usually occurs as a rounded corner (see specimen #3 above). As can be seen in image 004c, this face occurs as either completely truncating off the corner (just right of center) or partially truncating the corner (center of upper left quadrant). The majority of crystals, and nearly, if not all, of the smaller crystals do not show this face.

    The [110] and [101] crystal faces are stepped, or rippled, in the manner often seen in other a-Metatorbernite crystals. In this, the crystals are no different from their solitary bretheren.

    Diaphaneity - As can be seen in images 004b, 004c, and 004d, many of the crystals are quite transparent, lacking the usual optical density, and thus transluscence, of the darker variety of a-Metatorbernite. The darker, transluscent, variety is prevalent for most of the larger crystals, while the smaller crystals are lighter and more transparent, and not just due to their thinness. The under-side of the specimen is almost entirely these small crystals.

    Luster - The luster of all of the crystals is adamantine, which is usual for a-Metatorbernite. The scratches on the surface of several crystals is believed due to the collecting process.

    Several crystals show a rainbow diffraction pattern on their [001] face similar to the pattern produced by two optical flats placed together with a tissue paper seperating one edge. This is believed to be indicative of an extremely flat surface that is reflecting light off of molecular layers within the surface of the crystal. This is the first time that Metatorbernite, or any uranium or thorium mineral, has shown this. It does not photograph, due to glare, but can be seen by eye when the light falls upon certain crystals' [001] surface at just the correct angle.

    Physical Properties - Weight: 15.22 grams

     

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