Barroisite

Formula:  [] (CaNa)Mg₃AlFe(Si₇Al)O₂₂(OH)₂

Origin of name:  For Charles Barrois, French petrologist

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: a = 9.759 Å, b = 17.921 Å, c = 5.290 Å, b = 104.49°

Colour:  Green; semitransparent

Diaphaneity: Semitransparent

Luster:  Vitreous

Habit:  As rims on other amphibole crystals

Hardness:  5 to 6

Specific gravity:  3.2

Cleavage:  3; {110} perfect, {100} and {001} partings

Tenacity:

Streak:

Synonyms/varieties:

Comments:  Series with ferrobarroisite and with aluminobarroisite. Found in blueschist facies metamorphic rocks.