How to identify Bauxite

To correctly identify Bauxite (Bauxite), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Variable, commonly white, gray, yellow, brown, reddish-brown, or mottled.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, sometimes sub-vitreous in denser varieties.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often pisolitic (pea-sized concretions), oolitic (smaller, rounded grains), massive, earthy, or clay-like. Can be porous.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous to cryptocrystalline; individual mineral components (gibbsite, boehmite, diaspore) are microscopic and not typically visible as distinct crystals in hand samples.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is a rock composed of fine-grained minerals.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in tropical and subtropical regions through intense chemical weathering of aluminum-rich rocks, typically in well-drained upland areas or karst depressions. Found in lateritic profiles, often overlying parent rock or limestone.

Key Facts

Hardness

1 to 3 on Mohs scale (for individual mineral components, the rock itself is soft and friable).

Specific Gravity

2.0 to 2.5 (can vary depending on composition and porosity).

Crystal System

Not applicable for the rock itself; constituent minerals like gibbsite are monoclinic, boehmite and diaspore are orthorhombic.

Color

White, gray, yellow, brown, reddish-brown, mottled.

Luster

Dull, earthy, sometimes sub-vitreous.

Transparency

Opaque.

Fracture

Earthy, conchoidal (if dense), or irregular.

Cleavage

None (as a rock).

Composition

Mixture of aluminum hydroxide minerals (gibbsite Al(OH)3, boehmite γ-AlO(OH), diaspore α-AlO(OH)), iron oxides (goethite, hematite), clay minerals (kaolinite), and titanium oxides (ilmenite, anatase).

Physical characteristics

• Crystal Habit: Massive, earthy, pisolitic, oolitic, concretionary.
• Cleavage Type: None.
• Fracture Type: Earthy, irregular, sometimes sub-conchoidal.
• Tenacity: Friable to tough.
• Luster Type: Dull to earthy.

Explore Bauxite