Editorial Feature

Ahlfeldite – Occurrence, Properties, and Distribution

Ahlfeldite was named after Friedrich E. Ahlfeld (1892–1982), a German–Bolivian mining engineer and mineralogist.

Properties of Ahlfeldite

The following are the key properties of Ahlfeldite:

  • Cell Data
    • Space group: P21/n
    • a = 7.53(1)
    • b = 8.76(2)
    • c = 6.43(1)
    • β = 99°05 (15)’
    • Z = 4

  • Crystal Data
    • Monoclinic
    • Point group: 2/m
    • Rare crystals, to 1mm
    • Elongated along [001] or flattened parallel {110}, showing {110}, {011}, {032}, {103}, {101}
    • Crystalline crusts and spherical aggregates
    • X-ray powder pattern: 5.69 (100), 3.426 (80), 2.992 (75), 2.190 (75), 3.772 (60), 2.719 (60), 2.354 (50)

  • Chemical Composition
    Elements Content 1 Content 2
    SeO2 50.01 50.03
    NiO 30.24 16.84
    H2O 16.2 16.24
    CoO 3.55 16.89
    Total 100.0 100.00

  • Optical Properties
    • Optical class: Biaxial (-)
    • Pleochroism: X = pale green; Y = pale pink; Z = pink
    • Orientation: Y = b; Z^c = -16°
    • Dispersion: r < v, strong
    • α = 1.709(1); β = 1.752(1); γ = 1.787(2)
    • 2V(meas.) = 85°

  • Estimated Properties
    Electron density Bulk density (electron density) = 3.36 g/cm3
    note: Specific gravity of ahlfeldite = 3.52 g/cm3
    Photoelectric PEAhlfeldite = 36.69 barns/electron
    U = PEAhlfeldite x ρ electron density = 123.20 barns/cm3
    Fermion index Fermion index = 0.02
    Boson index = 0.98
    Radioactivity
    Ahlfeldite is not radioactive

How to Identify Ahlfeldite

Ahlfeldite can be identified in the field by its color variations, such as pink, brown, apple-green, and red. Its transparent form has {110} distinct, {103} distinct cleavage. This mineral has a vitreous luster, with a light green streak. The fracture on this mineral is brittle.

The density of ahlfeldite is 3.37 g/cm3, with a hardness of 2 to 2.5 - between gypsum and finger nail.

Global Distribution

Ahlfeldite is mainly distributed in Bolivia - From the Pacajake mine, Hiaco, 24km east-north-east of Colquechaca; and the El Dragon mine, 30km south-west of Cerro Rico de Potosi, Potosi.

Occurrence of Ahlfeldite and Useful Mineral Association

Ahlfeldite occurs in a rare alteration product of nickel-bearing selenides and sulfides.

It is often associated with minerals such as penroseite, olsacherite, chalcomenite, cerussite, anglesite, goethite, chalcomenite, olsacherite, and lepidocrocite.

References

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