USDA Texture Triangle
Definition
Ternary diagram that classifies soils by relative proportion of sand (2.0 to 0.05 mm), silt (0.05 to 0.002 mm) and clay (less than 0.002 mm) into 12 classes (sand, loamy sand, sandy loam, loam, silt loam, silt, clay loam, sandy clay loam, silty clay loam, sandy clay, silty clay, clay).
- Type
- Ternary classification diagram
- Axes
- Sand, silt, clay proportions by weight
- Sand range
- 2.0 to 0.05 mm
- Clay range
- Less than 0.002 mm
- Output classes
- 12 texture classes
Common questions
How is particle size measured before plotting on the triangle?+
Sieving separates the sand fraction, while sedimentation methods such as the hydrometer test measure the finer silt and clay fractions based on settling rate, and the resulting percentages are plotted to read off the texture class.
Why is texture class alone insufficient to individualise a soil to one location?+
Texture reflects only the sand-silt-clay ratio, which many geographically distant soils can share, so examiners combine it with mineralogy, colour, and trace evidence to build a stronger source comparison.
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