Eckermannite

Formula:   NaNa₂(Mg,Fe)₄AlSi₈O₂₂(OH)₂

Origin of name:   For C. von Eckermann, Swedish petrologist

Crystal system:   Monoclinic

Crystal class:   2/m

Twinning:

Unit cell: 

Colour:  Dark bluish green;

Diaphaneity:  translucent

Luster:   Vitreous

Habit:   Crystals long  prismatic; aggregates

Hardness:   5 to 6

Specific gravity:   3.0 to 3.17

Cleavage:   2; {110} perfect, {010} parting

Tenacity: 

Streak: 

Synonyms/varieties:

Comments:   Series with ferro-eckermannite