Gibbsite
ID: 62
Gibbsite
Chemical Formula
Al(OH)₃
Hardness (Mohs)
2.5 - 3
Crystal System
Monoclinic
Streak
White
Luster
Vitreous, sub-vitreous, pearly, dull, earthy.
Diaphaneity
Translucent
Color
White, light gray, light green, reddish white; reddish yellow (impure); blue, turquoise; purple. Ideally white; colored by mineral mixtures.
Crystal Habit / Mode of Occurrence
Typically found as small tabular crystals, often with a pseudohexagonal outline. Also occurs as botryoidal, stalactitic, or earthy masses and coatings.
Fun Facts
Gibbsite is named after Colonel George Gibbs, an American mineral collector whose extensive mineral collection was acquired by Yale University.