Ferroglaucophane

Formula:  Na₂(Fe,Mg)₃Al₂Si₈O₂₂(OH)₂

Origin of name:   From ferrous iron (Fe²⁺) and glaucophane

Crystal system:   Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: 

Colour:  Grayish, bluish black, lavender blue, azure blue

Diaphaneity:

Luster:  Vitreous to dull, sometimes pearly

Habit:  Crystals slender prismatic; massive, fibrous, columnar, granular

Hardness:  6

Specific gravity:  3.04 to 3.23

Cleavage:  1; {110} perfect

Tenacity: 

Streak:  Grayish blue

Synonyms/varieties:

Comments:  Series with glaucophane