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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

USDA texture triangle. percentages sum to 100. fine-earth fraction only.

40% sand + 40% silt + 20% clay = 100% · Loam. USDA size limits: sand 0.05–2 mm, silt 0.002–0.05 mm, clay <0.002 mm. Class colours are a key, not soil photographs.

Soil texture triangle

Use the proportions of sand, silt and clay to classify a soil, then explain how its texture affects water movement.

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Why it happens

Soil texture describes the proportions of sand, silt and clay. These fractions sum to 100%, and their mixture influences properties such as water retention and drainage.

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NPS fieldwork at Chesapeake and Ohio Canal National Historical Park. Texture describes the proportions of sand, silt and clay in the mineral soil.

Try a comparison

Change the mixture and follow its position between texture classes. Explain how the particle sizes differ, then distinguish texture from soil structure.

Reading the result

Texture is one influence on soil behaviour; structure, organic matter and compaction also affect water movement.

A common misunderstanding

A soil’s colour determines whether it is sand, silt or clay.

Texture depends on the proportions of mineral particles in defined size classes. Colour reflects other properties, including organic matter, iron compounds and drainage conditions. Two soils can therefore look similar while having different textures, and texture differs from the way particles are grouped into structure.

Cases

Exam language

Texture

In soil science, the proportions of sand, silt and clay in the mineral fraction. Texture influences pore sizes, drainage and water retention. It differs from soil structure, which describes how particles are arranged into aggregates.

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NPS scientists examine soil texture in the field. Sand, silt and clay proportions can be plotted on a ternary texture triangle; the photograph shows the sampled material and fieldwork.

Sand

Soil mineral particles 0.05–2 mm across in the USDA system. Other sediment classifications use a slightly different lower boundary.

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Sossusvlei dunes, Namib Desert. Wind transports loose sand by surface creep and saltation; the dunes record accumulated transport rather than individual grain paths.

Silt

Soil mineral particles 0.002–0.05 mm across in the USDA system, intermediate between clay and sand.

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NASA Landsat observation of the Thames estuary. The tidal river widens towards the North Sea; pale water reveals suspended material and shallow coastal water.

Clay

The finest soil mineral particles, less than 0.002 mm across in the USDA system. Their large surface area strongly affects water and nutrient retention.

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Kaolinite from Ixtassou, France, is a clay mineral. Clay as a soil texture means particles smaller than 0.002 mm; mineral identity and particle size are different properties.

Loam

A USDA soil-texture class containing a mixture of sand, silt and clay; loam is not defined as equal thirds of the three fractions.

USDA texture triangle

A chart used to classify soil from its percentages of sand, silt and clay. The three fractions must add to 100%, and their intersection identifies a texture class. Texture describes particle size, while structure describes how particles form aggregates.

Ternary plot

A triangular diagram showing three proportions whose sum is 100%. Each corner represents one pure component. In the soil-texture triangle, a sample’s sand, silt and clay percentages locate its texture class.

Adjust parameters

Sand %40Clay %20