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| Introduction | |
| The complete mineral list | |
| Ore minerals | |
| Calcsilicate minerals | |
| Secondary minerals | |
| Parker shaft minerals | |
| Selected species | |
| Franklinite | |
| Willemite | |
| Zincite | |
| Hodgkinsonite | |
| Roeblingite | |
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Ore minerals
Overview
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Typical granular Franklin ore. Franklinite (black), willemite (yellow-green) and zincite (red). Polished surface. Width 1 cm. |
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Three minerals were mined as zinc ore at the Franklin-Sterling mining district: franklinite, a Zn-Mn-Fe spinel; willemite, a Zn-silicate; and zincite, a Zn-oxide.
These three minerals occurred within the Zn-Mn-Fe orebodies at Franklin and Sterling Hill, primarily in segregated ore units, as described by Frondel and Baum (1974).
These three minerals were found in tens of millions of tons at both Franklin and Sterling Hill, New Jersey. Franklinite and zincite are uncommon elsewhere.
The three minerals are often found in compact granular (gneissic) form, with zincite an occasional constituent.
Large single-phase masses of these three minerals were also encountered, as were euhedral crystals, some measuring many cm across. Generally the most perfectly formed crystals are microscopic in size, however.
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Banded ore from the Franklin mine. Typical gneissic banded ore. Grain size ranges from 1 to 3 mm. Franklin, NJ. Width 16 cm. |
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Banded ore detail. Close-up view of the sample shown above. Franklinite (black), zincite (red), willemite (yellow-green), minor tephroite (gray to brown). Franklin, NJ. Width 3 cm. |
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Tephroite (gray), zincite (red), willemite (yellow-green), and franklinite (black). Note the large grain size (to 1 cm) typical of many attractive preserved samples. Franklin, NJ. Width 6 cm. |
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The ore units also contained much tephroite and other Mn-silicates. In general, phases in the ore units are less siliceous and more metal-rich than those in the Ca-silicate units. The ore units also contain a smaller number of species.
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Manganosite (green), zincite (red) and franklinite (black). Manganosite is a rare mineral encountered very sparingly in the Franklin mine. Polished thick section. Width 2 cm. |
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Some additional information on the ore minerals is provided by species name (listed on the left). For further information on the ore minerals, consult Dunn (1995).
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