Franklinite
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Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron series, with the formula Zn²⁺Fe₂³⁺O₄.
As with another spinel member magnetite, both ferrous and ferric iron may be present in franklinite samples. Wikipedia
Crystal system: Cubic
Category: Oxide minerals; Spinel group; Spinel structural group
Cleavage: None; indistinct octahedral parting in four directions
Color: black
Crystal class: Hexoctahedral (m3m); H-M symbol: (4/m 3 2/m)
Crystal habit: octahedral
Formula (repeating unit): ZnFe2O4