Zincite

Formula:	ZnO
Crystal system:	Hexagonal	Space group:	P63mc

	Zincite. Thin, micaceous habit. Franklin, NJ. Width 6 cm.

Occurence

Zincite is moderately abundant, particularly in localized occurrences, at both Zn-Mn-Fe orebodies at Franklin and Sterling Hill, New Jersey. It contains roughly 80% Zn by weight, but was the least common of the three zinc ore minerals from the district.

Most zincite occurs in massive or granular form, euhedral crystals are very rare. 

In zincite-bearing hand specimens of normal granular ore, zincite concentration often follows gneissic banding present.

Zincite is hexagonal, and is based on hexagonal closest packing of zinc atoms in an oxygen matrix.

	Zincite crystal structure. Two layers of zinc filled coordination polyhedra shown.		Zincite-rich ore. Note concentration parallel to ore banding. With willemite (green) and franklinite (black). Franklin, NJ. Width 7 cm.

Euhedral crystals, when found, are often dull-faced and simple in form. They generally show a hexagonal pyramid and base. Much oscillation between pyramidal forms is commonly present in microscopic crystals.

	Zincite crystals. After figures 25 and 26 in Palache (1935).					Zincite crystal. Franklin, NJ. Crystal height 1 cm.

Zincite is also found as distorted, rounded crystals of up to many centimeters in size embedded in similarly coarsely crystallized calcite. 

Such distorted crystals are often fractured in samples from Sterling Hill, but some from Franklin are less fractured, and show a very pronounced lamellar habit.

Pure ZnO is white in color (and sold as the pigment "zinc white"). However, zincite from the district ranges from dark red to almost black, through orange and pale-yellow in finely fractured or microcrystalline samples. 

	Hetaerolite inclusions in zincite. Plane polarized light. Franklin, NJ. Width 0.2 mm.

Zincite is commonly yellow in thin-section.

Manganese, present in amounts up to 7% by weight, is in part responsible for the red coloration. 

Additionally, much zincite contains microscopic inclusions of hetaerolite, which can also darken the apparent color.

Zincite is not generally fluorescent, but certain unusual light-colored varieties may fluoresces yellow under long-wave and short-wave ultraviolet light.

For further information on zincite, see Dunn (1995).

 

	Zincite. Distorted dark-red crystals in calcite matrix, with tephroite (pink, lower right). Sterling Hill, NJ. Width 30 cm.

 

	Lamellar zincite. Distorted crystals in calcite matrix. Franklin, NJ. Width 8 cm.		Lamellar zincite. Stack of plates showing some warping. Franklin, NJ. Width 5 cm.

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