Boltwoodite – Occurrence, Properties, and Distribution

Boltwoodite was named after Bertram Borden Boltwood (1870-1927), radiochemist of Yale University, New Haven, Connecticut, USA, who devised the U-Pb method of measuring geologic time.

Properties of Boltwoodite

The following are the key properties of boltwoodite:

  • Cell Data
    • Space group: P21
    • a = 7.073(2)
    • b = 7.064(1)
    • c = 6.638(1)
    • β = 105°45 (1)’
    • Z = 2
  • Crystal Data
    • Monoclinic
    • Point group: 2
    • Radiating acicular to fibrous, elongated along [010], to 1 cm
    • X-ray powder pattern: 6.81 (100), 3.40 (90), 2.95 (80), 3.54 (70), 2.91 (70), 6.40 (50), 5.45 (50)
  • Chemical Composition
    Elements Content 1 Content 2 Content 3
    UO3 68.5 67.19 66.64
    SiO2 14.8 13.27 14.00
    K2O 9.4 7.83 10.97
    H2O 6.9 - 8.39
    LOI - 6.91 -
    Na2O 0.4 2.54 -
    CaO - 1.59 -
    Fe2O3 - 0.52 -
    Total [100.0] 99.85 100.00
  • Optical Properties
    • Optical class: Biaxial (-)
    • Pleochroism: Weak; X = colorless; Y = Z = yellow; anomalous blue interference colors
    • α = 1.668-1.670; β = 1.695-1.696; γ = 1.698-1.703
    • 2V(meas.) = Large
  • Estimated Properties
    Electron density Bulk density (electron density) = 3.19 g/cm3
    note: Specific gravity of Boltwoodite = 3.62g/cm3
    Photoelectric PEBoltwoodite = 1,429.97barns/electron
    U=PEBoltwoodite x ρ electron density= 4,558.55 barns/cm3
    Fermion index Fermion index = 0.0071947992
    Boson index = 0.9928052008
    Radioactivity Boltwoodite is radioactive

How to Identify Boltwoodite

Boltwoodite can be identified in the field by its color variations between yellow and light yellow. Its opaque form has {010} perfect and {001} distinct cleavage. This mineral has a vitreous-pearly luster with white streak. The density of boltwoodite is 3.6 g/cm3, with a hardness of 3.5-4 - between that of a copper penny and fluorite.

Global Distribution

Boltwoodite is distributed in the following places:

  • USA - From the Delta mine, Emery Co., Utah; the New Method mine, near Amboy, San Bernardino Co., California; in the Marshall Pass district, at the Little Indian No. 36 mine, Gunnison Co. and the Lookout No. 22 mine, Saguache Co., and in Unaweep Canyon, Mesa Co., Colorado; in the Green Monster mine, Goodsprings district, Clark Co., Nevada; and in the Williams quarry, near Easton, Northampton Co., Pennsylvania
  • Namibia -Exceptionally developed at the Raossing mine, near Swakopmund
  • Rwanda - At Karago
  • Argentina - From Quebrada del Tigre, Cordoba Province, and near Guandacol, La Rioja Province
  • Scotland - From near Dalbeattie, Kirkcudbrightshire
  • Australia - From near Myponga, South Australia
  • Japan- In the Togo mine, Tottori Prefecture

Occurrence of Boltwoodite and Useful Mineral Association

Boltwoodite occurs in the outer silicate zone of alteration surrounding hydrated uranyl oxides incrusting primary uraninite; and also filling fractures at some distance from primary uraninite. It also occurs in pegmatite and Colorado-Plateau-type sandstone uranium deposits.

Boltwoodite is often associated with minerals such as uraninite, becquerelite, fourmarierite, gypsum, fluorite, and phosphouranylite.

References

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