Formula: Al2Si2O5(OH)4
Origin of name: For Baron d'Halloy, first observer
Crystal system: Monoclinic
Crystal class: m
Twinning:
Unit cell:
Colour: Colourless, white; may be tinted yellowish, brownish, reddish or bluish by impurities
Diaphaneity:
Luster: Pearly to dull earthy
Habit: Tubular (on microscopic scale); massive, compact or mealy
Hardness: 2 to 2.5
Specific gravity: 2 to 2.2
Cleavage: None
Tenacity:
Streak:
Synonyms/varieties:
Comments: Polymorphous with dickite, kaolinite and nacrite; occurs as hallooysite-7Ǻ and -10Ǻ polytypes
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