Magnesioriebeckite

Formula:  []Na₂(Mg,Fe)₃Fe₂Si₈O₂₂(OH)₂

Origin of name:  From magnesium and riebeckite

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning: 

Unit cell: 

Colour:  Dark blue to black

Diaphaneity:  Translucent to opaque

Luster:  Vitreous to silky

Habit:  Crystals long prismatic, striated along elongation; massive, fibrous to asbestiform, columnar, granular

Hardness:  5

Specific gravity:  3.19

Cleavage:  1; {110} perfect

Tenacity: 

Streak: 

Synonyms/varieties:

Comments:  Series with riebeckite and with magnesio-arfvedsonite