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Chemical Formula | (Zn,Fe2+)(Fe3+)2O4 This is the pure formula for Franklinite. However, since Franklinite usually contains a significant amount of manganese as both the first and second element, its formula is officially recognized as: (Zn,Fe2+,Mn2+)(Fe3+,Mn3+)2O4 |
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Composition | Zinc iron oxide, usually with a significant amount of manganese | ||||||||
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Variable Formula | (Zn,Fe2+,Mn2+)(Fe3+,Mn3+)2O4 | ||||||||
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Color | Black | ||||||||
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Streak | Brownish-black to brownish-red | ||||||||
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Hardness | 5½ - 6½ | ||||||||
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Crystal Forms and Aggregates |
(Isometric) Occurs as octahedral crystals, usually embedded and somewhat rounded. Rarely as dodecahedral crystals. Also occurs grainy, massive, and as rounded pebbles. | ||||||||
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Transparency | Opaque | ||||||||
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Specific Gravity | 5.0 - 5.2 | ||||||||
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Luster | Metallic, submetallic | ||||||||
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Cleavage | None. May exhibit parting. | ||||||||
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Fracture | Subconchoidal to uneven | ||||||||
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Tenacity | Brittle | ||||||||
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Other ID Marks | Slightly attracted to magnetic fields ("paramagnetic") | ||||||||
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In Group | Oxides ; Multiple oxides ; Spinel group | ||||||||
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All About | Franklinite is named after the locality of
Franklin, New Jersey, where it is found. It is only found
in Franklin and the neighboring town of Ogdensburg. There
are no other localities for this mineral. It is usually
associated with brilliantly fluorescent Calcite and
Willemite, and may also occur with orange Zincite. Franklinite is sometimes classified as a variety of Magnetite, but it is an individual mineral species. |
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Uses | Franklinite was a very important ore
of zinc, together with the other zinc minerals at the
Franklin and Sterling Hill mines. Now, however, those
mines are no longer active, so Franklinite is no longer
used as an ore of zinc. Large crystals of Franklinite are popular among collectors. |
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Striking Features | Locality, mineral associates, and weak attraction to magnetic fields | ||||||||
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Popularity (1-4) | 2 | ||||||||
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Prevalence (1-3) | 2 | ||||||||
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Demand (1-3) | 2 | ||||||||
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Distinguishing Similar Minerals |
Magnetite - strongly attracted to magnetic
fields Spinel - not attracted to magnetic fields, has a white streak |
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Commonly Occurs With |
Calcite, Willemite, Zincite, Rhodonite, Andradite, Magnetite | ||||||||
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Noteworthy Localities |
The only places where this mineral exists is Franklin and Ogdensburg (Sterling Hill), both in Sussex Co., New Jersey. In these two localities it occurs in great abundance. | ||||||||
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Picture Icon Links |
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Picture Links | 1. Large crystal in Calcite 2. Small, rounded crystals in Calcite 3. Distorted crystal mass 4. Single octahedral crystal |
