THE MINERAL FRANKLINITE

Chemical Formula: (Zn, Fe, Mn)(Fe, Mn)2O4, Zinc Iron Manganese Oxide
Class: Oxides and Hydroxides
Group: Spinel
Uses: Important ore of zinc and manganese and as mineral specimens.
Specimens

Franklinite is one of the minerals found at Franklin, New Jersey, a world famous locality that has produced many formerly unknown and exotic mineral species. It is found in large enough quantity to serve as a ore of zinc and manganese, two important strategic and industrial metals. It forms octahedral crystals that are typical of the spinel group of minerals. Specimens from Franklin often contain the rounded black grains of franklinite surrounded by white calcite and/or greenish willemite with a sprinkling of red zincite. Specimens of this exotic and interesting mineral are truly valued by mineral collectors.

PHYSICAL CHARACTERISTICS:

Color is dark black.
Luster is metallic.
Transparency: Crystals are opaque.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include octahedrons often with dodecahedral faces modifing the edges of the octahedron. The modifing can lead to an overall rounding of the crystal. Also as massive and granular.
Cleavage is absent.
Fracture is conchoidal.
Hardness is 6
Specific Gravity is 5.0 - 5.2 (slightly above average for metallic minerals)
Streak is reddish brown.
Other characteristics: Slightly magnetic.
Associated Minerals include willemite, zincite, calcite, rhodonite and other minerals found at Franklin, New Jersey.
Notable Occurrences are limited to the world famous mines at Franklin, New Jersey, USA from where franklinite gets its name.
Best Field Indicators are crystal habit, streak, associations with other zinc minerals and locality.