Gibbsite
Al(OH)3

     Gibbsite is very rare at MSH. It is the monoclinic trimorph of nordstrandite and bayerite.

PHYSICAL CHARACTERISTICS:

Color is usually colorless to pale pink, white for the powdery
   masses.
Luster is vitreous to greasy.
Diaphaneity is transparent to opaque.
Crystal System is monoclinic; P21/c.
Crystal Habits include compact powdery masses and sharp
   equant, blocky or wedge-shaped crystals to 2mm.
Cleavage {001} is tough.
Fracture is tough.
Hardness is 2.5 - 3.5
Specific Gravity is approximately 2.4 g/cm3.
Streak is white.
Associated Minerals include natrolite.
Distinguishing Features: no evident ones.
Origin: Named in 1822 after Col. George Gibbs (1776-1833),
   mineralogist, who donated a collection of 12,000 specimens to
   Yale University; a founder of the American Journal of Science.

CLASSIFICATION:

Dana System
# 6.3.1.1

Strunz Classification
# IV/F.2-10

REFERENCES:
MinRec 21:312 (1990), Dana 8:280-281 (1997)

DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:

MSH
¤¤¤

PE
--

AP
¤¤

MX
--

SS
¤¤

MC
¤¤

HF
--

BR
--

SX
--

FR
--

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