Laterite

Hardness: Varies greatly, can be soft and earthy or hard and rock-like (iron-rich varieties can be 5-6 on Mohs). Color: Reddish-brown to dark red, yellow, or orange due to high iron oxide content. Luster: Dull to earthy. Crystal structure: Amorphous or cryptocrystalline; does not typically exhibit distinct crystal forms. Cleavage: None. Specific gravity: 2.5-3.0.

Laterite forms in tropical and subtropical regions with high rainfall and distinct wet and dry seasons. It is a residual product of intense and prolonged chemical weathering of underlying parent rocks (like basalt, granite, gneiss, or shale). During weathering, soluble bases and silica are leached away, leaving behind insoluble oxides of iron and aluminum (hematite, goethite, gibbsite). This process is called laterization. The geological age is typically Cenozoic to recent, as it requires specific ongoing climate conditions.

Laterite is traditionally used as a building material, especially for bricks (cut directly from the ground and hardened on exposure to air). Iron-rich laterites are often mined as iron ore. Bauxite, the primary ore of aluminum, is often found in lateritic deposits. It can also be used as a road base material.

The word "laterite" is derived from the Latin word "later," meaning brick, referring to its ability to be cut into brick-like blocks. It is responsible for the characteristic red soils seen in many tropical regions, such as parts of Australia, India, and Africa. Angkor Wat in Cambodia notably utilizes laterite as a primary building material.

In the field, laterite is identified by its distinctive reddish-brown to dark red color, relatively low density for a rock, and often porous or earthy texture. It can sometimes be quite hard and blocky. It is commonly found in tropical and subtropical regions worldwide, including Brazil, India, West Africa, and Australia. Collectors might seek laterite with visible concretions or interesting textural features. Its presence often indicates a highly weathered landscape.