Brockite – Occurrence, Properties, and Distribution

Brockite was named after Maurice R. Brock from the U.S. Geological Survey, who supplied the first specimen. It belongs to the rhabdophane group.

Properties of Brockite

The following are the key properties of brockite:

  • Cell Data
    • Space group: P6222
    • a = 6.96(3)
    • b = 6.40(3)
    • Z = 3

  • Crystal Data
    • Hexagonal
    • Point group: 622
    • Rarely as stubby hexagonal prisms, to 50µm
    • Commonly granular radial, in very fine-grained massive aggregates, cryptocrystalline earthy
    • X-ray powder pattern: 3.03 (vsb), 4.37 (s), 2.83 (s), 2.15 (s), 3.47 (m), 1.86 (m), 6.06 (mw)

  • Chemical Composition
    Elements Content 1 Content 2
    ThO2 44.7 23.9
    P2O5 24.7 34.6
    RE2O3 6.9 23.8
    CaO 10.2 10.6
    H2O 7.8 -
    ZrO2 - 4.0
    CO2 3.2 -
    UO2 - 3.1
    SrO 1.4 -
    BaO 1.1 -
    Total [100.0] 100.0

  • Optical Properties
    • Optical class: Uniaxial (+)
    • Orientation: Parallel extinction, positive elongation
    • ω = 1.680(2)
    • ε = 1.695(2)

  • Estimated Properties
    Electron density Bulk density (electron density) = 3.60 g/cm3
    note: Specific gravity of brockite = 3.90 g/cm3
    Photoelectric PEBrockite = 753.16 barns/electron
    U=PEBrockite x ρ electron density= 2,710.28 barns/cm3
    Fermion index Fermion index =0.0003228265
    Boson index = 0.9996771735
    Brockite is radioactive

How to Identify Brockite

Brockite can be identified in the field by its color variations, such as white, light yellow, dark reddish-brown, and reddish-brown. Its translucent form has no cleavage. This mineral has a vitreous, greasy luster. The fracture on this mineral is conchoidal. The density of brockite is 3.7 - 4.1 g/cm3, with a hardness of 3 - 4 - between calcite and fluorite.

Global Distribution

Brockite is distributed in the following places:

  • USA - In a prospect pit about 1km east of the Bassick mine, Querida, Wet Mountains, and at the Hardwick mine and Nightingale shaft, Custer Co. Colorado; in the Bear Lodge Mountains, Crook Co. Wyoming; from the Diamond Creek district, Lemhi Co. Idaho and the Lemhi Pass district, Idaho-Montana; found in Monroe Canyon, Sevier Co. Utah; from the Laughlin Peak area, Colfax Co. New Mexico; in the Rawhide Mountains, Mohave Co. Arizona
  • Canada - At Mont Saint-Hilaire, Quebec
  • Japan - From Atagoyama, Shionhira, Shin-yashikiike, and Ishizuka, Ishikawa district, Fukushima Prefecture
  • Turkey - From Kizilcaoren

Occurrence of Brockite and Useful Mineral Association

Brockite occurs in a rare accessory mineral in granite and granite pegmatites. It is often associated with minerals such as monazite, bastnasite, apatite, xenotime, thorite, rutile, hematite, and zircon.


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