Formula: (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,H2O]
Origin of name: From state of Illinois
Crystal system: Orthorhombic
Crystal class: 2/m
Twinning:
Unit cell:
Colour: White and pale colours
Diaphaneity:
Luster: Dull
Habit: Massive, extremely fine-grained
Hardness: 1 to2
Specific gravity: 2.6 to 2.9
Cleavage: 1; {001} perfect
Tenacity:
Streak:
Synonyms/varieties:
Comments: A group of mica-clay minerals, not a distinct species
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