Formula: Zn²⁺Fe³⁺₂O₄

Species: Oxides

Colour: Black

Lustre: Metallic, Sub-Metallic

Hardness: 5½ – 6

Specific Gravity: 5.07 – 5.22

Crystal System: Isometric

Member of: Spinel Subgroup > Oxyspinel Group > Spinel Supergroup

Name: Named in 1819 by Pierre Berthier for the type locality of Franklin Furnace (now Franklin Borough), New Jersey. Benjamin (1706-1790), American statesman, was also the first important USA scientist who investigated electricity and was an inventor of bifocal lenses for eye glasses, the fuel efficient Franklin Stove, lightening rods, the carriage odometer, and the glass harmonica (musical instrument).

Co-Type Localities: Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA; Trotter Mine, Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA; Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex County, New Jersey – USA

Isostructural with: Hetaerolite, Magnetite