Soil classification of composite soils exclusively based on the particle size distribution is known as textural classification.

To use the textural classification chart, for a given percentage of three constituents forming a soil, lines are drawn parallel to three sides of the equilateral triangle.

Based on HRB system, the soil is divided into 7 primary groups, designated as A-1, A-2…A-7.

As the system is classified based on size, it is preferable to use the word ‘silt size’ and ‘clay size’ in place of simply ‘silt’ or ‘clay’.

Soil occurring in nature is composed of a different percentage of sand, silt, and clay size particles.

A triangle, having equal length of sides (i.e. Equilateral triangle) is used in textural classification chart.

Since properties of clay soils is less dependent on particle size distrubution(textural classification) and more dependent on size it is best suited for clay soil.

Triangular classification of U.S. public road administration is a commonly used system for textural classification.

Indian standard classification (IS: 1948-1970) is based on the M.I.T. system.

For general engineering purposes, soil can be classified in terms of particle size, textural and unified soil.