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ZINCITE [ Oxides and Hydroxides ]

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ZnO, zinc manganese Oxide

An ore of zinc and as mineral specimens

Zincite is a one locality mineral. Well actually that is not true. It is found at several localities around the world; and is rare and inconspicuous at all but one general site. That site is the famous zinc and manganese mines of the Sterling Hill and Franklin, New Jersey, USA area. Many rare minerals are found there and zincite although rare everywhere else, is far from rare there. So abundant was zincite that it was quickly exploited and became an important ore of zinc.
The structure of zincite consists of tetrahedrons of ZnO4. The tetrahedrons in zincite all are oriented in one direction and produce the hexagonal (six fold rotational) symmetry. The major axis is symmetrically polar and results in a hemimorphic crystal structure. In other words, there is no symmetry element, like a mirror or two fold rotational axis, perpendicular to the major axis and thus crystal faces on top of the crystal are not repeated on the bottom of the crystal. Hemimorphic crystals have different looking tops from their bottoms, as if they never completed the opposite, symmetrical, side; therefore the term hemimorphic or half shape. Other minerals besides zincite that have a hemimorphic character are the tourmalines, hemimorphite (what’s the first clue?), greenockite and wurtzite; among others.

Physical Characteristics

Colour: orange-yellow to deep red or brown
Luster: adamantine
Transparency: crystals are commonly translucent more rarely transparent
Crystal System: hexagonal; 6 m m
Crystal Habits: include rarely well shaped, over all, hemimorphic pyramidal crystals sometimes with an hexagonal prism terminated by the basal face of a pedion on one side and the sharp point of the pyramid on the other. Usually found as rounded granular crystals; also massive in veins and lamellar
Cleavage: good in three directions (prismatic)
Fracture: conchoidal
Hardness: 4
Specific Gravity: 5.4 – 5.7 (slightly heavy even for metallic minerals)
Streak: orange-yellow
Other: There is a basal parting
Associated Minerals: include calcite, rhodonite, willemite, franklinite, tephorite, pyroxmangite and other rare Sterling Hill and Franklin, New Jersey minerals
Major Occurrences: include the Sterling Hill and Franklin, New Jersey, USA locations where it is found in abundance. Some occurrences from where zincite is found but in much scarcer quantities include Tuscany, Italy; Tsumeb, Namibia; the Dick Weber Mine, Colourado, USA; Poland, Spain and Tasmania, Australia
Best Indicators: luster, colour, occurrence, associations, cleavage, parting and streak
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