FRANKLINITE

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Cubic
    Chemistry : ZnFe2O4
    Rarity : Rare to very rare

Franklinite belongs to the group of spinels with a normal structure. It is a rare mineral present in zinc-bearing metal deposits that have undergone contact metamorphism. It combines with zincite and willemite. It can also be found in certain slags. It owes its name to its location of discovery : the Franklin mine (New Jersey, USA) and also to honor the name of Benjamin Franklin, politician, physicist and inventor of the lightning rod who gave its name to the city. Franklinite occurs in granular or compact masses like magnetite, rarely in octahedral crystals with often rounded faces. Its luster is metallic, sometimes dull, its color brown-black to black. It is occasionally a zinc ore.

Main photo : 5 cm edged franklinite from Franklin Mine, Franklin, Sussex County, New Jersey, USA © Rock Currier

Franklinite from Sterling Mine, Sterling Hill, New Jersey, USA © Terry Burtzlaff
Franklinite and Willemite from Sterling Mine, New Jersey, USA © Steven Kuitem
Franklinite from Sterling Mine, Sterling Hill, New Jersey, USA © Jeff Krueger
Franklinite from Franklin Mine, Franklin, Sussex County, New Jersey, USA © Carl Carnein

Franklinite in the World

The only locality to have provided crystals are the zinc mines of Franklin and Sterling Hill (New Jersey), where the octahedrons reached 15 cm on edge.

Franklinite in France

Franklinite is not present in the French undeground.

Twinning

Twins are known on {111}.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 5.5 to 6
Density : 5.07 to 5.22
Fracture : Irregular to conchoidal
Streak : Red-brown to black

TP : Opaque
RI : 2.36
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric acid


Magnetism : None
Radioactivity : None