18 Photos
Gahnite
Chemical Formula	ZnAl2O4
Species	Oxides & Hydroxides
Crystal System	Isometric
Mohs Scale	7-8
Specific Gravity	4.38-4.60
Color	Dark green, bluish green, blue to indigo, yellow to brown
Streak	Grey
Luster	Vitreous
Refractive Index	n = 1.79–1.80
Diaphaneity	Translucent to nearly opaque
Cleavage	Indistinct parting on
Fracture	Irregular/Uneven, Conchoidal
Crystal Habit：Typically octahedra, rarely as dodecahedra also assive to granular

Gahnite, ZnAl₂O₄, is a rare mineral belonging to the spinel group. It forms octahedral crystals which may be green, blue, yellow, brown or grey. It occurs in Falun, Sweden where it is found in pegmatites and skarns, contact metamorphic rocks. Other occurrences include Charlemont, Massachusetts; Spruce Pine, North Carolina; White Picacho district, Arizona; Topsham, Maine; and Franklin, New Jersey in the United States.

It was first described in 1807 for an occurrence in the Falu mine, Falun, Dalarna, Sweden, and named after the Swedish chemist, Johan Gottlieb Gahn (1745–1818), the discoverer of the element manganese. It is sometimes called zinc spinel.