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16.72: Zincite

  • Page ID
    6541
  • Zincite

    Zincite
    Chemical composition (Zn,Mn)0
    Crystal system Hexagonal
    Habit Pyramidal (hemihedral); massive
    Cleavage Perfect on {10-10}; Parting on {0001}
    Fracture Conchoidal
    Hardness 4
    Optic nature Uniaxial +
    Refractive index 2.013 – 2.029
    Specific gravity 5.66
    Lustre Sub-adamantine to resinous
    Fluorescence Pale yellow (extremely rare)

     

    Habit

    Pyramidal crystals, distinctly hemimorphic; massive.

     

    Chemical composition

    Zinc oxide, ZnO. Usually with minor amounts of manganese (less than 7%), and minor to trace amounts of iron, magnesium, and aluminum.

     

    Diagnostics

    Because of its high specific gravity, zincite is unlikely to be confused with any other gem material.

     

    Color

    Deep red, deep orange. Manganese is the coloring agent. Green zincite has been observed in nature but to date has not been found in sizes sufficient to facet.

     

    Magnification

    Black submetallic inclusions of franklinite or hetaerolite (both oxides containing zinc and manganese) are common.

     

    Specific Gravity

    5.66 (measured) 5.67 (calculated)

     

    Refractive Index

    nε = 2.029, nω = 2.013

     

    Treatments

    None known.

     

    Phenomenon

    Zincite may, in extremely rare instances, display a pale yellow fluorescence in long-wave ultraviolet light. This has not yet been documented in cut stones.

     

    Synthetics

    Synthetic zincite flooded the US market in the late 1980’s and 1990’s, available in a rainbow of colors from pale green to green, pale red to deep red, and yellow to deep orange synthetic. This material was derived from the smokestacks of a metal refinery in Silesia, Poland, where it had crystallized over many years from volatized zinc oxide. Zincite is also grown in laboratories by several techniques, including hydrothermal, Czochralski pull, and vapor deposition (sublimation) methods.

     

    Imitations

    None reported.

     

    Occurrence

    As a primary and secondary mineral in metamorphosed zinc-iron-manganese ore deposits. Zincite is actually very rare, except at the zinc mines of Franklin and Ogdensburg in Sussex County, New Jersey, where it is one of the three primary ore minerals. Enormous tonnages were mined between circa 1830 and circa 1980.

     

    Sources

    • Anthony, John W., Bideaux, Richard A., Bladh, Kenneth W., and Nichols, Monte C. (1990): Handbook of Mineralogy: Mineral Data Publishing, Tucson, Arizona
    • Dunn, Pete J. (1995) Franklin and Sterling Hill, New Jersey: the world’s most magnificent mineral deposits
    • Palache, C. (1935), Minerals of Franklin and Sterling Hill, New Jersey, USG Professional Paper 180
    • Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Seventh edition