Minerals · common

Gibbsite

Gibbsite is aluminum hydroxide, Al(OH)3, a soft, typically white to gray mineral that forms as a weathering product in tropical and subtropical soils and serves as the principal ore mineral of aluminum within bauxite deposits. It commonly occurs as fine-grained, earthy masses or crusts rather than well-formed crystals, though occasional tabular pseudohexagonal crystals do develop in cavities. It is named after American mineral collector George Gibbs, whose collection helped found early American mineralogy.

Photo: Robert M. Lavinsky · Wikimedia Commons · CC BY-SA 3.0

Gibbsite properties at a glance

Type	Minerals
Chemical formula	Al(OH)3
Mohs hardness	2.5–3.5
Crystal system	Monoclinic
Luster	Vitreous, pearly on cleavage, dull when earthy
Streak	White
Cleavage	Perfect basal {001}
Fracture	Uneven
Specific gravity	2.3–2.4
Transparency	Transparent to translucent
Common colors	White, Gray, Greenish, Reddish
Rarity	common

Geology & background

Gibbsite forms through intense chemical weathering of aluminosilicate rocks, particularly in humid tropical climates where heavy rainfall leaches out silica and other elements faster than aluminum, concentrating it into laterite and bauxite deposits. Major bauxite-producing regions rich in gibbsite include Jamaica, Australia's Weipa and Darling Range districts, and parts of West Africa and Brazil, where deep lateritic weathering profiles have developed over millions of years. It also occurs as a secondary mineral in hydrothermal veins and pegmatite cavities, though this occurrence is far less economically important than the bauxite form.

Rockhounds rarely seek gibbsite for crystal beauty, since it is typically massive, chalky, or earthy, but well-formed pseudohexagonal plates from certain pegmatites do attract specialist collectors. Its overwhelming importance lies in industry, since gibbsite-rich bauxite gets refined through the Bayer process into alumina, the raw material for aluminum metal. Anyone examining tropical soil profiles or lateritic weathering zones is likely encountering gibbsite even without recognizing it as a distinct mineral.

How to identify Gibbsite

Gibbsite is usually white, gray, or pale green to pale yellow with a dull to pearly luster and a white streak, occurring most often as earthy, chalky, or stalactitic masses rather than distinct crystals. Hardness is low, around 2.5 to 3.5, easily scratched with a fingernail or copper coin, and it shows perfect cleavage on the rare crystal faces that do form. When crystals appear, they are thin, tabular, and pseudohexagonal. Massive gibbsite is easily confused with other clay-like aluminum or iron hydroxide minerals such as boehmite or goethite without laboratory testing.

Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
Use multiple photos when possible, including a fresh surface and a close view of texture.

Where Gibbsite is found

Reported from multiple localities worldwide; verify locality against specimen provenance when available.

How much is Gibbsite worth?

Entry-level specimen	$2
Typical collector specimen	$20
Premium specimen	$150+

Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.

Common uses

Collector specimens
Education
Field identification
Industrial or lapidary use when suitable

Interesting facts

Gibbsite is the primary aluminum-bearing mineral refined into alumina and eventually aluminum metal through the industrial Bayer process.
The mineral honors George Gibbs, an early American mineral collector whose specimens helped establish mineralogy as a serious science in the United States.
Vast quantities of gibbsite form silently in tropical soils today, a slow weathering process that has been building bauxite deposits for millions of years.