Spessartine

Formula: Mn₃Al₂(SiO₄)₃

Origin of name: after locality Spessart, Bavaria, Germany

Crystal system: cubic

Crystal class: 4/m -3 2/m

Twinning:

Unit cell: a = 11.63 Å

Colour: red, reddish orange, yellowish brown, reddish brown

Diaphaneity: 

Luster: vitreous

Habit: crystals dodecahedrons or trapezohedrons, faces often striated, embedded grains, massive, compact

Hardness: 7 to 7.5

Specific gravity: 3.8 to 4.25

Cleavage: 1; {110} parting, may be distinct

Tenacity: brittle

Streak: white

Synonyms/varieties: spessartite, johnstonotite (Ca-rich variety)

Comments: member of the garnet group, series with almandine and with pyrope