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The Mineral gibbsite

White Gibbsite From Type Locality

Gibbsite is one of the three component minerals of the economically important aluminum ore Bauxite. Gibbsite was first discovered in 1820 by Chester Dewey (1784-1867) of Williams College, Massachusetts. It was first thought to be Wavellite, but a year later it was determined to be a separate mineral species and was subsequently named Hydrargillite. It was then renamed Gibbsite in 1822 by John Torrey (1796-1873) in honor of George Gibbs (1776-1833) of New Haven, a noted mineralogist whose important collection was acquired by Yale University.

Chemical Formula

Al(OH)3

Color

White, gray, colorless, light green, green, greenish-blue, yellowish-brown, reddish-brown

Crystal System

Monoclinic

Properties

Streak
White
Hardness
2.5 - 3.5
Transparency
Transparent to translucent
Specific Gravity
2.4
Luster
Vitreous, dull. Pearly on cleaved surfaces.
Cleavage
1,3
Fracture
Uneven
Tenacity
Brittle

Crystal Habits

Crystals, which are flattened tabular and sometimes twinned, are usually only microscopic. Almost always in botryoidal, stalactitic, pisolitic, or in other globular habits. Also in massive earthy form and encrusting.

Additional Information

Composition
Basic aluminum hydroxide
In Group
Oxides; Hydroxides
Striking Features
Low specific gravity, globular habits, and mode of occurence.
Environment
As a secondary mineral forming in the weathered surface zones in clay deposits and limestones, as well as low-silica igneous rocks and pegmatites.

Uses

Gibbsite, being an important component of Bauxite, is an important ore of aluminum.

Noteworthy Localities

Localities where collection-worthy Gibbsite specimens have been found are very sporadic. The type locality where this mineral was first described is Richmond, Berkshire Co., Massachusetts. An outstanding, aesthetic green botryoidal form resembling Prehnite has been recently described in Xianghualing, Linwu, Hunan Province, China; and a one time find of bright greenish-blue Gibbsite first thought to be Hemimorphite occurred in Baoshan, Yunnan Province, China. Light bluish-green botryoidal crusts of Gibbsite came from the Kamariza Mines, Agios Konstantinos, Lavrion District, Greece; and microscopic colorless crystals, sometimes twinned from the Saga 1 Quarry, Mørje, Telemark, Norway. White Gibbsite is found associated with bright orange-red Crocoite, and sometimes even as an alteration of the Crocoite, at Dundas, Tasmania, Australia.

Common Mineral Associations

Boehmite, Diaspore, Calcite, Natrolite, Goethite, Doyleite

Distingushing Similar Minerals

Smithsonite, Wavellite, Hemimorphite, and Prehnite all have a higher specific gravity.

gibbsite Photos



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