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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. |
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Chemical Formula |
Al(OH)3 |
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Composition |
Basic aluminum hydroxide |
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Color |
White, gray, colorless, light green, green, greenish-blue, yellowish-brown, reddish-brown |
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Streak |
White |
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Hardness |
2.5 - 3.5 |
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Crystal System |
Monoclinic |
Crystal Forms
and Aggregates |
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.
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Transparency |
Transparent to translucent |
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Specific Gravity |
2.4 |
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Luster |
Vitreous, dull. Pearly on cleaved surfaces. |
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Cleavage |
1,3 |
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Fracture |
Uneven |
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Tenacity |
Brittle |
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In Group |
Oxides; Hydroxides |
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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.
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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2 |
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Demand (1-3) |
1 |
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Gibbsite, being an important component of Bauxite, is an important ore of aluminum.
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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.
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