franklinite

Franklinite is a mineral belonging to the spinel group, with the chemical formula (Zn,Fe,Mn)(Fe,Mn)2O4. It is a zinc iron manganese oxide. Franklinite is typically found as an opaque, black to brownish-black crystalline solid. It often forms well-defined crystals, commonly dodecahedral or octahedral in habit. The mineral is opaque and has a metallic to submetallic luster. Its streak is typically dark brown to black. Franklinite is relatively hard, ranking between 5.5 and 6.5 on the Mohs scale of hardness. It is insoluble in common acids.

The most famous and historically significant deposits of franklinite are located in Franklin and Sterling Hill, New Jersey, USA. These deposits are also notable for containing numerous other rare and unusual minerals, including willemite and zincite, which often occur in close association with franklinite. The mineral was named after the town of Franklin, New Jersey, where it was first described. Franklinite serves as a primary ore of zinc, and historically, it was smelted to extract this metal. Its unique mineral assemblage and geological context have made the Franklin-Sterling Hill district a world-renowned location for mineral collectors and geologists.