Coutinhoite

Thorium analog of Weeksite		 IMA-2003-025
Uranium
Thorium		 -
(Dana Classification Number)
(Images) -
(Strunz ID)

Property Data Remarks
Named for: José Moacyr Vianna Coutinho (1924- ), Professor of Mineralogy and Petrography at the Instituto de Geociencias of Universidade de Sao Paulo, Brazil
Alternate
    Name(s):
  		•  
    Mineral Class:
     
       
         
    		 
    Chemical
        Formula:    		 ThxBa(1-2x)(H2O)y(UO2)2Si5O13 · H2O

    [with: 0 <= x <= 0.5; and 0 <= y <= (2+x)]

    Empirical formula (based on Si + P = 5):

    (Th0.30Ba0.19K0.07Ca0.04)S0.60(UO2)2.00(Si4.92P0.08)S5.00O12.91 · 2.86H2O    		  
    Chemical
        Composition:
    Barium: (Ba) 10.209%
    Hydrogen: (H) 0.974%
    Oxygen: (O) 14.624%
    Silicon: (Si) 20.876%
    Thorium: (U) 8.624%
    Uranium: (U) 17.693%
    		by weight

    (based on
    x = 0.25
    y = 1.0)
    Molecular
        Weight:    		 672.662 daltons (amu)
    Specific
        Radioactivity:

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

    Specific Activity Dose Rate
    Becquerels Curies milliRems/hour microSieverts/hour
    × 10 × 10    

    Estimated Average Annual Exposure: 360 mRem (3.6 milliSieverts)
    Crystalography:
    System: Orthorhombic
    Axial Ratios: a:  
    b:  
    c:  
    Cell Dimensions: a: 14.1676 Å
    b: 14.1935 Å
    c: 35.754 Å
    Z: 16
    a:   °
    b:   °
    g:   °
    V: 7189.7 Å3
    DenCalc: 3.839
    Optical: biaxial negative
    a 1.620(3)
    ß 1.627(3)
    ? 1.629(3)
    2V (meas.) = 40(5)°
    2V (calc.) = 56.1°
    dispersion r < v strong
    orientation Y = c
    H-M Symbol:  
    Space Group: Cmmb (?)
    X-Ray Diffraction:
      By Intensity ( I/Io )    		 (1): Å
    (0.): Å
    (0.): Å
    		Probably isostructural with Weeksite
    Habit:
  • flaky micro crystals up to 10 µm long and up to about 0.5 µm thick
  • irregular aggregates with very small curved scales
    		•   
    Cleavage:
    [001]  
    [010]  
    [100]  
    		 
    Fracture: Brittle  
    Moh's
        Hardness:    		 1.5  
    Density:   grams/cm3
    Color: Light yellow or Yellow  
    Streak: Yellow  
    Luster: Waxy to Silky  
    Diaphaneity: Transparent to Translucent  
    Pleochroism:
    (x): Yellow
    (y:)
    (z:) > Y
    		 
    Ultra Violet
        Fluorescence:    		 Non-Fluorescent  
    Magnetism: Non-magnetic  
    Occurance:
  • A secondary hydrothermal mineral in pegmatite
    		•   
    Associated
        Minerals:

    Meta-Autunite, and intimately associated with Weeksite, Phosphuranylite, Meta-uranocircite and Uranocircite on Muscovite and Microcline.

    Minerals   -   Uranium & Thorium
    mineral links

    		These are minerals known to be found with Coutinhoite
    Localities:

    Extremely rare

    Coutinhoite Localities
    Notes:

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

    Crystals are probably metamic.

    Thorium - analog of Weeksite

    Coutinhoite Images

    Specimen #1
      Photo by Tom Loomis,
    Dakota Matrix Minerals
    		 Photo by Tom Loomis,
    Dakota Matrix Minerals
    		  
    Lavra do Urucum (Lavra do Tim), Galiléia, Governador Valadares, Rio Doce, Minas Gerais, Southeast Region, Brazil

    Specimen Notes

    Occurrence -   No matrix is present. Specimen is nearly microscopic in size.

    Crystals - Any crystals, if present, are sub-microscopic, and too small to be seen under 30X magnification.

    Appearence - The specimen is quite small, and only general observations can be made.

    Diaphaniety - Specimen is opaque.

    Luster - The specimen appears to have a earthy, of clay-like, luster. This may be due to sub-microscopic crystal size.

    Color - The color of the specimen is a very pale yellow-white.

     

    Specimen Physical Properties
    Size (smaller than sand grains)   (compare to its large gell capsule containment)
    Weight: (several milligrams)   (too small to accurately measure)
    g-Radiation Level:   cmp   msieverts background: 20 cpm