Gibbsite is a primary mineral component of bauxite and typically appears in white, waxy, or pearly tabular crystals or botryoidal masses. It is commonly found in tropical weathering zones or as a secondary mineral in hydrothermal alteration environments.
Is this gibbsite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch gibbsite with a known reference. Gibbsite sits at Mohs 2.5-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, pearly on cleavage surfaces, dull in aggregates.
- 4Match the color rangeCompare against the expected color range: bluish, green, green white, gray, gray white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: earthy, spherical, stalactitic.
Often confused with
Gibbsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous, pearly on cleavage surfaces, dull in aggregates on Gibbsite and pearly to dull earthy on Kaolinite.
How to tell apart: Diaspore is the harder of the two (Mohs 6.5-7 vs. 2.5-3.5); luster reads vitreous, pearly on cleavage surfaces, dull in aggregates on Gibbsite and adamantine, vitreous, pearly on cleavage faces on Diaspore.
Often found alongside gibbsite
Minerals reported to co-occur with gibbsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al(OH)₃
- Mohs hardness
- 2.5-3.5
- Density
- 2.40 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous, pearly on cleavage surfaces, dull in aggregates
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Earthy, spherical, stalactitic
- Cleavage
- {001}, perfect
- Rarity
- Common
- Uses
- Collector, Ore of aluminum
- Host rock
- A typical product of weathering of aluminous minerals, common in lateritic soils and bauxite
Where rockhounds find gibbsite
Classic worldwide localities
- Richmond, Berkshire Co., Massachusetts, USA
- Unionville, Chester Co., Pennsylvania, USA
- Champion mine, White Mountains, Mono Co., California, USA
- Toomsboro, Wilkinson Co., Georgia, USA
- Saramenha, Ouro Prêto, Minas Gerais, Brazil
- Paramaribo, Surinam
Field-hunting tip
Where it forms: A typical product of weathering of aluminous minerals, common in lateritic soils and bauxite. If you start seeing diaspore, böhmite, corundum in float, you are in the right ground. Typical habit: earthy, spherical, stalactitic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find gibbsite on the map
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