Gahnite

Formula:  ZnAl₂O₄

Origin of name:  For Johan Gahn, Swedish chemist

Crystal system:  Cubic

Crystal class:  4/m -3 2/m

Twinning:

Unit cell:

Colour:  Greenish black, bluish black, dark bluish green, brown, yellowish

Diaphaneity:  Translucent

Luster:  Vitreous to greasy

Habit:  Crystals octahedral, rarely cubic or dodecahedral; massive, coarse granular to compact; rounded grains

Hardness:  7.5 to 8

Specific gravity:  4.61

Cleavage:  1; {111} parting indistinct

Tenacity:

Streak:  Greyish

Synonyms/varieties:

Comments:  Series with spinel and with hercynite