Formula: Ca2(Fe,Mg)4Al(Si7Al)O22(OH,F)2
Origin of name: From iron {Latin ferrium) and magnesiohornblende
Crystal system: Monoclinic
Crystal class: 2/m
Twinning: On {100}, simple or lamellar
Unit cell: a = 9.96 Ǻ, b = 18.19 Ǻ, c = 5.32 Ǻ, β = 104.9°
Colour: Green to dark green, greenish brown, black
Diaphaneity:
Luster: Vitreous
Habit: Crystals long to short prismatic; massive, compact, granular, columnar, bladed or fibrous
Hardness: 5 to 6
Specific gravity: 3.41
Cleavage: 3; {110} perfect, {001} and {100} parting
Tenacity: Subconchoidal to uneven; brittle
Streak:
Synonyms/varieties: Barkevikite, hornblende
Comments: Series with magnesiohornblende
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