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

In the particle soil classification system, soils are arranged to the grain size.

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.

The purpose of soil classification is to arrange various types of soils in to groups according to their engineering or agricultural properties.

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.

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

Particle size classification used only as a designation of particle sizes, and do not signify the naturally occurring types which are mixtures of a particle of different sizes.

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

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

Highway research board classification system is also known as public road administration (PRA) system.