Boltwoodite

 IMA-GP
Uranium 53.3.1.5
(Dana Classification Number)
(Images) 8/B.34-60
(Strunz ID)

Property Data Remarks
Named for: Bertram Borden Boltwood (1870-1927), radiochemist of Yale University, New Haven, Connecticut, USA, who devised the Uranium-Lead method of measuring geologic time
Alternate
    Name(s):
  • Nenadkevite
    		•   
    Mineral Class:
    Silicates
      Nesosilicates
    "Insel" silicates with anions unfamiliar to tetraheders
    Uranyl-"Insel" silicates with [UO2]2+ - [SiO4]4-
        Sklodowskite - Uranophane - Kasolite series
    		 
    Chemical
        Formula:    		 K2(UO2)2(SiO3)2(OH)2 . 3H2O  
    Chemical
        Composition:
    Hydrogen: (H) 0.94%
    Oxygen: (O) 27.96%
    Potassium: (K) 9.11%
    Silicon: (Si) 6.54%
    Uranium: (U) 55.45%
    		by weight
    Molecular
        Weight:    		 429.24 daltons (amu)
    Specific
        Radioactivity:

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

    Specific Activity Dose Rate
    Becquerels Curies milliRems/hour microSieverts/hour
    9.9265 × 1004 2.68 × 10-06 1.37 136.85

    Estimated Average Annual Exposure: 360 mRem (3.6 milliSieverts)
    Crystalography:
    System: Monoclinic - Sphenoidal
    Axial Ratios: a: 1.9201
    b: 1
    c: 1.7296
    Cell Dimensions: a: 13.71 Å
    b: 7.14 Å
    c: 12.35 Å
    Z: 6
    b: 102.2°
    V: 1,181.63 Å3
    DenCalc: 3.62
    H-M Symbol: 2
    Space Group: P21
    X-Ray Diffraction:
      By Intensity ( I/Io )    		 (1): 6.81 Å
    (0.9): 3.4 Å
    (0.8): 2.95 Å
    		Boltwoodite
    Crystals
    (Observed)
    Habit:
  • Crusts
  • Tufts of fine acicular crystals,
    • on uranium bearing sandstones    		  
    Cleavage:
    [001] Distinct
    [010] Perfect
    [001]  
    		 
    Fracture:    
    Moh's
        Hardness:    		 3.5 - 4  
    Density: 3.6 - 4.3
        (dependant on water content)    		 grams/cm3
    Color: Yellow to pale yellow  
    Streak: White  
    Luster: Vitreous to Silky or Pearly  
    Diaphaneity: Translucent  
    Pleochroism:
    (x): Colorless
    (y:) Colorless
    (z:) Colorless
    		 
    Ultra Violet
        Fluorescence:
    Long Wave: Fluorescent
    Short Wave: Fluorescent
    		 
    Magnetism: Non-magnetic  
    Occurance:
  • Formed from the oxidation and alteration of the outer silicate alteration zone surrounding hydrated uranyl oxides incrusting primary uraninite.
  • Filling fractures at some distance from the primary uraninite.
  • Forms crusts that are found on uranium bearing sandstones.
    		•   
    Associated
        Minerals:

    Brochantite, calcite, gypsum, Becquerelite, Uraninite and other primary uranium minerals (and an unnamed uranyl-silicate)

    Minerals   -   Uranium & Thorium
    mineral links

    		 
    Localities:

    Rare

    Boltwoodite Localities
    Notes:

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

    Boltwoodite Images

    Specimen #1
    (001a) (001b) (001c)
    Rössing mine, Swakopmund District, Namibia


    Specimen Notes

    Occurance - The Boltwoodite occurs on a substrate of Calcite on a silicate host rock. This is in agreement with the hot radicals theory of the occurance of Uranyl minerals.

    Crystals - The Boltwoodite is in a radial cluster of crystals. The crystals are seen to occur in two general forms. The first is the basic monoclinic form, varying in thickness from very thin (fairly common), to a square cross section (most common), to where the thickness is considerably greater than its width (rare).

    The second form, seen in the center of image 001a, is quite rare, with only one occurance being seen. This crystal form is modeled at the bottom of the Boltwoodite crystal page.

    Luster - The luster of the Boltwoodite crystals is vitreous. They appear 'earthy' when the specular light reflection is not seen.

    Diaphaneity - The Boltwoodite is translucent to nearly opaque. None of the crystals are transparent.

      -  

     

    Specimen Physical Properties
    Size   cm   cm   cm
    Weight: x grams    
    g-Radiation Level:   cmp   msieverts background: 20 cpm