FRANKLINITE
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.