Zincite Value, Price, and Jewelry Information

ZINCITE: Franklin, New Jersey (gem ~1, rough 2 inches long). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Zincite

Zincite is a very rare mineral, essentially restricted to one important locality. Well, terminated crystals were found only up to about 3-4 inches, but larger masses, weighing several pounds, have been encountered in the ore bodies. These are not especially interesting, but cabochons with red zincite, green willemite, and white calcite, peppered with black franklinite, are unique to the Franklin occurrence and are extremely beautiful as well as highly fluorescent. Spheres have also been cut from this material. Cut zincite is one of the rarest of all gemstones. It is seldom completely transparent; usually it is slightly cloudy or translucent.

Zincite Information

Data Value
Name Zincite
Colors Dark red, brownish red, deep yellow, orange-yellow; colorless if pure.
Crystallography Hexagonal. Crystals hemimorphic and very scarce; massive, cleavable, compact, grains.
Refractive Index 2.013-2.029
Luster Subadamantine to adamantine.
Hardness 4-4.5
Fracture Conchoidal
Specific Gravity 5.68
Birefringence 0.016
Cleavage Perfect 1 direction but difficult
Dispersion 0.127
Stone Sizes Cabochons have been cut from granular zincite in white calcite from Franklin. Faceted gems of Franklin material are very rare, maximum about 20 carats. Most of the (few) faceted zincites are in the 1-3 carat range. Smithsonian Institution (Washington, D.C): 20.1 and 12.3 (red, New Jersey). American Museum of Natural History: 16.27 (red, Franklin, New Jersey). Philadelphia Academy of Natural Science: 12.7 (red, New Jersey). Private Collection: 3.28 (clean, superbly cut, probably wor1d‘s finest). Harvard University: 3.08 (red, New Jersey).
Luminescence None.
Luminescence Present No
Transparency Transparent to opaque.
Formula

ZnO + Mn.

Pleochroism

None.

Optics

o = 2.013; e = 2.029. Uniaxial (+).

Optic Sign Uniaxial +

Streak: Orange-yellow.

Optics: o= 2.013; e = 2.029.

Uniaxial (+).

Occurrence: In metamorphosed limestone and zinc ores.

Franklin, New Jersey: only major locality; massive red ore, also in crystals up to 4 inches long, but these were found only in secondary calcite veins.

Poland: Spain; Tasmania.

Comments: Zincite is a very rare mineral, essentially restricted to one important locality. Well, terminated crystals were found only up to about 3-4 inches, but larger masses, weighing several pounds, have been encountered in the ore bodies. These are not especially interesting, but cabochons with red zincite, green willemite, and white calcite, peppered with black franklinite, are unique to the Franklin occurrence and are extremely beautiful as well as highly fluorescent. Spheres have also been cut from this material. Cut zincite is one of the rarest of all gemstones. It is seldom completely transparent; usually it is slightly cloudy or translucent.

Name: In allusion to the composition.

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