Franklinite is an ore of zinc and manganese, two important metals that are industrial. This is a collector that is common mineral because of its typical associations with fluorescent minerals such as Calcite and Willemite. Franklinite is rarely available as a treasure that is faceted it is opaque, black and extremely brittle.

Franklinite is mostly known from the kind locality of Franklin, nj-new jersey, United States Of America but in addition found in a few other locations around the globe such as Långban, Värmland, Sweden; Hranicná, Czech Republic; Nayzatas, Dzhumart, and in the Ushkatyn deposits, Atasui area, Kazakhstan; the marble that is pereval, near Slyudyanka, Sayan Mountains, south of Lake Baikal, Siberia, Russia.

Category: Spinel structural group
Formula: ZnFe2O4
Ferrous Zincate
Crystallography: Isometric – Hexoctahedral
Crystal Habit: Typically as octahedral crystals, dodecahedral less common, cubic rare; commonly with rounded edges, to 22 cm; may be modified. Also exsolved within other minerals; coarse to fine granular, massive.
Twinning: Twinning on {111} as both twin and composition plane, the spinel law, common.


Cleavage: None observed; Parting on [111], fair
Fracture: Irregular/Uneven, Conchoidal
Tenacity: Very Brittle
Hardness (Mohs): 5.5 – 6.0
Density: 5.07 – 5.22 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive
Other: Strongly to Weakly Magnetic; the variation in composition ratio of Zn:Fe results in a variable degree of magnetism.


Color: Black, Iron-Black, Brownish Black, Reddish Black, may be tarnished; in reflected light, White to Gray, with dark Red internal reflections.
Transparency: Opaque, Translucent in fine fragments
Luster: Metallic, Sub-Metallic
Refractive Index: 2.36(2)  Isotropic 
R: (400) 19.2, (420) 19.2, (440) 19.2, (460) 19.2, (480) 19.2, (500) 19.1, (520) 19.0, (540) 18.6, (560) 18.2, (580) 17.8, (600) 17.4, (620) 17.1, (640) 16.8, (660) 16.6, (680) 16.4, (700) 16.3
Birefringence: 0.000  Isotropic
Pleochroism: None