Rhönite

Formula: Ca₂(Fe,Mg,Ti)₆(Si,Al)₆O₂₀

Origin of name: after locality Rhön district, Germany

Crystal system: triclinic

Crystal class: -1

Twinning: common on {010}

Unit cell: a = 10.48 Å, b = 10.92 Å, c = 9.17 Å, a = 101.4°, b = 97.0 °, g = 129.7°

Colour: brown to black

Diaphaneity: 

Luster: semimetallic

Habit: 

Hardness: 5 to 6

Specific gravity: 3.64

Cleavage: 

Tenacity: 

Streak: 

Synonyms/varieties:

Comments: from a few localities and a meteorite