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

n_ε = 2.029, n_ω = 2.013

Treatments

None known

Phenomenon

Zincite may, in extremely rarely 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