Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula Zn2+Fe23+O4.

As with another spinel member magnetite, both ferrous (2+) and ferric (3+) iron may be present in franklinite samples.

At its type locality, franklinite can be found with a wide array of minerals, many of which are fluorescent.

In these rocks, it forms as disseminated small black crystals with their octahedral faces visible at times.

It may rarely be found as a single large euhedral crystal.