Soils

Soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics.


Soil is composed of particles of broken rock that have been altered by chemical and environmental processes that include weathering and erosion. Soil differs from its parent rock due to interactions between the lithosphere, hydrosphere, atmosphere, and the biosphere. It is a mixture of mineral and organic constituents that are in solid, gaseous and aqueous states. Soil is commonly referred to as dirt.
Soil particles pack loosely, forming a soil structure filled with pore spaces. These pores contain soil solution (liquid) and air (gas). Accordingly, soils are often treated as a three state system. Most soils have a density between 1 and 2 g/cm³. Soil is also known as earth: it is the substance from which our planet takes its name. Little of the soil composition of planet Earth is older than the Tertiary and most no older than the Pleistocene. In engineering, soil is referred to as regolith, or loose rock material.

 

A (soil), B (laterite, regolith), C (saprolite), C (bedrock)

Laterite

are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty - red because of iron oxides. They develop by intensive and long lasting weathering of the underlying parent rock.

Tropical weathering (laterization) is a prolonged is a process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land areas with laterites was or is between the tropics of Cancer and Capricorn.