Afwillite – Occurrence, Properties and Distribution

Afwillite is named after Alpheus Fuller Williams (1874-1953), the General Manager of DeBeers Consolidated Mines, South Africa. It was discovered in the year 1925 at the Dutoitspan Mines, South Africa.

Properties of Afwillite

The key physical properties of Afwillite are as below:

  • Cell Data
    • Space group: Cc
    • a = 16.278(1)
    • b=5.6321(4)
    • c=13.236(1)
    • Z = 4
  • Crystal Data
    • Monoclinic
    • Point group: m
    • Crystals – prismatic, elongated and striated II [010], to 11 cm, many tabular on {100} and {201}; in radial fibrous spherulites; massive
    • X-ray powder pattern: Kimberly, South Africa
      2.83 (100), 6.61 (90), 3.18 (90), 2.73 (90), 3.28 (70), 2.15 (70), 2.34 (60)
  • Chemical Composition
    Elements Content 1 Content 2 Content3
    SiO2 33.96 34.65 35.09
    Al2O3, Fe2O3 0.60 - -
    MgO - trace -
    CaO 49.28 48.94 49.13
    F - 0.18 -
    H2O+ 15.89 16.08 15.78
    H2O- 0.12 0.01 -
    -O=F2 - 0.10 -
  • Optical Properties
    • Transparent
    • Optical class- Biaxial (+)
    • Lustre – Vitreous
  • Estimated Properties
    Electron density Bulk density (electron density)= 2.66 g/cm3
    note: Specific gravity of Afwillite = 2.62 g/cm3
    Photoelectric PEAfwillite = 4.90 barns/electron
    U=PEAfwillite x ρelectron density= 13.06 barns/cm3
    Fermion index Fermion index = 0.008
    Boson index = 0.99
    Radioactivity
     
    GRapi = 0 (Gamma Ray American Petroleum Institute Units)
    Afwillite is not radioactive

How to Identify Afwillite

The color of afwillite varies from colorless to white. It is brittle by nature and exhibits a vitreous lustre. Its hardness varies from 3 to 4.

Global Distribution

Afwillite is widely distributed in the following locations:

  • South Africa – from Dutoitspan Diamond Mine, Kimberly;Wessels Mine, Cape Province
  • Ireland – from Scawt Hill,Antrim
  • Germany – Schellhopf, Eifel District; Zeilberg, Bavaria
  • Italy- from Campomorto, Lazio
  • Israel – from Nahal Ayalon
  • USA – from Crestmore, Riverside, Calofirnia
  • Japan- from Mihara mine, Okayama Perfecture.

Occurrence of Afwillite and Useful Mineral Association

Afwillite is a product formed during the metamorphism of limestones. It is often associated with minerals such as natrolite, merwinite, ettringite, brucite, calcite, foshagite, portlandite and hillebrandite.

References

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