Bauxite (Pisolitic Bauxite)

Physical Properties

Hardness: 1-3 (soft, earthy) to 5-6 (pisoliths). Color: Reddish-brown, yellow, or grey. Luster: Dull to earthy. Structure: Pisolitic (concentric pea-sized spheres). Cleavage: None. Specific Gravity: 2.0-2.5.

Formation & Geological History

Formed through the intense chemical weathering of rocks (like granite or basalt) in hot, humid tropical or subtropical climates. This process, called lateritization, leaches away silica and results in an accumulation of aluminum oxides. Most deposits are of Cenozoic or Mesozoic age.

Uses & Applications

The primary ore for aluminum production. It is also used in the manufacture of abrasives, refractories, chemicals, and cement.

Geological Facts

Bauxite is not a mineral but a rock composed primarily of minerals like gibbsite, boehmite, and diaspore. The distinctive 'ball' look comes from pisoliths, which are accretionary grains that grow in soil zones.

Field Identification & Locations

Identify by its distinctive 'pea-like' or 'pitted' circular textures called pisoliths. It is typically found in tropical regions like Australia, Guinea, Brazil, and Jamaica. Collectors look for well-defined pisoliths and rich coloration.

Identified on: 4/13/2026

Mode: Standard