Osumilite

Formula: (K,Na)(Fe,Mg)₂(Al,Fe)₃(Si,Al)₁₂O₃₀.H₂O

Origin of name: after locality Osumi, old place name, Kyusyu, Japan

Crystal system: hexagonal

Crystal class: 6/m 2/m 2/m

Twinning: rare on {21-30}

Unit cell: a = 10.15 Å, c = 14.26 Å

Colour: dark blue to black

Diaphaneity: 

Luster: vitreous

Habit: crystals short prismatic, elongated on c-axis, or tabular, to 5 mm

Hardness: 

Specific gravity: 2.64

Cleavage: none

Tenacity: brittle

Streak: 

Synonyms/varieties:

Comments: osumilite-(Mg) is a distinct species with Mg dominant in the second cation position in the formula, series between osumilite and osumilite-(Mg)