Editorial Feature

Nontronite – Occurrence, Properties and Distribution

Nontronite is named after the place at which it was discovered, near Saint-Pardoux, Nontron, France. It was discovered in the year 1827.

Properties of Nontronite

The key physical properties of Nontronite are as below:

  • Cell Data
    • Space group: C2/m
    • a = 5.23 – 5.26
    • c=14.8 – 15.8
    • Z = n.d
  • Crystal Data
    • Monoclinic
    • Point group: 2/m
    • Crystals – rarely as small bladed crystals, radial or reticulated, spherulitic, commonly cryptocrystalline, claylike massive.
    • X-ray powder pattern: Nontron, France
      15.4 (vs), 4.56 (vs), 2.64 (vs), 2.56 (vs), 1.52 (vs), 2.43 (s), 1.72 (s)
  • Chemical Composition
    Elements Content 1 Content 2
    SiO2 48.82 40.25
    TiO2 - 0.03
    Al2O3 4.30 5.50
    Fe2O3 35.88 29.44
    MgO 0.35 0.53
    CaO - 2.29
    H2O+ - 7.25
    H2O- - 15.09
    H2O 9.66 -
  • Optical Properties
    • Translucent to opaque
    • Optical class- Biaxial
    • Lustre – Waxy, resinous, dull
  • Estimated Properties
    Electron density Bulk density (electron density)= 2.28 g/cm3
    note: Specific gravity of Nontronite = 2.28 g/cm3
    Photoelectric PENontronite = 7.45 barns/electron
    U=PENontronite x ρelectron density= 17.00 barns/cm3
    Fermion index Fermion index = 0.01
    Boson index = 0.99
    GRapi = 0 (Gamma Ray American Petroleum Institute Units)
    Nontronite is not radioactive

How to Identify Nontronite

Nontronite appears as a dull, resinous and waxy mineral. The color varies from greenish yellow, olive green and brownish green. This mineral has a hardness of 1.5 – 2, between talc to gypsum. It is non-fluorescent.

Global Distribution

Nontronite is found in the following locations:

  • France – from Saint-Pardoux, Froland, Norway
  • Sweden – from Vittensten
  • Russia- from Okhansk
  • Germany – from Saxony, Geilsdorf and Wolkenstein
  • Madagascar – from Faratsiho
  • Australia – from Burra copper mine, Tamworth copper mine, Attunga, New South Wales
  • USA – Spruce Pine District, North Carolina, Washington, Crestmore, Riverside, Woody Kern, California.

Occurrence of Nontronite and Useful Mineral Association

Nontronite occurs as a weathering product of basalts, kimberlites and other ultramafic igneous rocks; in poorly-drained volcanic ash soils, in some hydrothermally altered mineral deposits, midocean ridge basalts and contact metamorphosed limestones. It is usually associated with minerals such as quartz, opal, hornblende, mica, kaolinite, olivine and pyroxenes.


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