Franklinite is an important zinc ore mineral having the formula (Zn,Fe,Mn)(Fe,Mn)2O4 - zinc iron manganese oxide.  It has a metallic luster, black color, no cleavage, and is slightly magnetic.  Most crystals have a truncated rounded shape.  Well formed crystals are nice octahedrons (double square pyramids).


The only significant franklinite occurrence on Earth is in northern New Jersey, in the famous Mesoproterozoic-aged Franklin Marble.  In that unit, the rare zinc minerals franklinite and zincite (red ZnO) are abundant and mined as a source of Zn metal.


Franklinite crystals (most are 1 to 2 mm in size) from residue of crushed zinciferous marble (zinc ore: franklinite-zincite-willemite-calcite rock).  From the Mesoproterozoic-aged Franklin Marble at the Sterling Hill Mine in Franklin, northern New Jersey, USA.



Photo gallery of franklinite



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