Ericssonite

Formula:   NaMn₂(FeO)Si₂O₇(OH)

Origin of name:   For J. Ericsson, Swedish-American engineer

Crystal system:   Monoclinic

Crystal class:   2/m

Twinning:

Unit cell: 

Colour:  Reddish-black

Diaphaneity:

Luster:

Habit:   Massive; embedded plates

Hardness:   4.5

Specific gravity:   4.21

Cleavage:   2; {100} perfect, {011} distinct

Tenacity: 

Streak:   Brown

Synonyms/varieties:

Comments:   Dimorphous with orthoericssonite; weakly magnetic