Cordierite - Occurrence, Properties, and Distribution

Cordierite is a magnesium iron aluminium cyclosilicate mineral, discovered in 1813. It was named after Pierre Louis A. Cordier, a French mining engineer and geologist, who first described it.

Properties of Cordierite

The following are the key properties of Cordierite:

  • Cell Data
    • Space Group: Cccm
    • a = 17.079(3)
    • b = 9.730(2)
    • c = 9.356(2)
    • Z = 4

  • Crystal Data
    • Orthorhombic, pseudohexagonal
    • Point Group: 2/m 2/m 2/m:
    • Crystals: short prismatic, striated || [001], to 18cm; typically granular to compact, massive
    • Twinning: Common on {110}, {130}, simple, lamellar, cyclical
    • X-ray Powder Pattern: 8.45 (100), 8.52 (95), 3.039 (65), 3.035 (65), 3.132 (55), 3.012 (55), 4.09 (50)

  • Chemical Composition
    Elements Content 1 Content 2
    SiO2 50.2 49.46
    Al2O3 33.5 33.58
    MgO 12.8 12.06
    H2O+ 1.69 1.71
    FeO 0.84 2.12
    Na2O 0.26 0.14
    CaO 0.23 0.03
    Fe2O3 0.14 0.14
    K2O 0.14 0.30
    H2O- 0.12 0.10
    MnO 0.06 0.08
    TiO2 <0.01 0.01
    Total 99.98 99.73

  • Optical Properties
    • Optical Class: Biaxial (+) or (-)
    • Pleochroism: X = pale yellow, green; Y = violet, blue-violet; Z = pale blue
    • Orientation: X = c; Y = a; Z = b
    • Dispersion: r < v; weak to marked
    • Absorption: Z > Y > X
    • α = 1.527-1.560
    • β = 1.532-1.574
    • γ = 1.537{1.578
    • 2V(meas.) = 35°-106°

  • Estimated Properties
    Electron density Bulk density (electron density) = 2.63 g/cm3
    note: Specific gravity of Cordierite = 2.65 g/cm3
    Photoelectric PECordierite = 1.65 barns/electron
    U = PECordierite x ρElectron density = 4.32 barns/cm3
    Fermion index Fermion index = 0.01
    Boson index = 0.99
    Radioactivity
    Cordierite is not radioactive

How to Identify Cordierite

Cordierite can be either colorless or can occur in a range of colors, from gray to yellow, violet, and pale blue. It is non-fluorescent, with white streak, and vitreous luster. It has a transparent to translucent appearance, and has poor cleavage. Its fractures are brittle, and are characterized by smooth, curving surfaces. It can be identified by its massive granular or prismatic crystal forms.

The relative hardness of cordierite is 7, and its average density is 2.65 g/cm3.

Global Distribution

Cordierite is distributed in the following places:

  • Bodenmais, Bavaria, Germany
  • OrijÄarvi and LeppÄavirta, Finland
  • KragerÄo, near Tvedestrand, Norway
  • Mt. Bity district, south of Antsirabe, Madagascar
  • Treasure Casket claims, Fungure Reserve, Zimbabwe
  • Namib, Namibia
  • Gem gravels of Sri Lanka
  • Tiruchchirappalli and Coimbatore, Tamil Nadu, India
  • Harts Range, Northern Territory, Australia
  • Richmond, Cheshire Co. New Hampshire, USA
  • Haddam, Middlesex Co. Connecticut
  • Thompson, Manitoba, Canada

Occurrence of Cordierite and Useful Mineral Association

Cordierite occurs in detrital, mafic igneous rocks and granites, high-grade regionally metamorphosed schists, granulites, and gneisses. It also occurs in thermally metamorphosed argillaceous sediments.

The minerals that are closely associated with cordierite include andalusite, garnet, spinel, corundum, biotite, muscovite, potassic feldspar, and sillimanite.

References

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