Soil texture triangle

Loading photograph

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

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
Read the sand, silt and clay axes and locate the selected mixture in the texture triangle. Check that its fractions add to 100%.
Open Observe
02
Tinker
Change the mixture and follow its position between texture classes. Explain how the particle sizes differ, then distinguish texture from soil structure.
Open Tinker
03
Explain
Explain why changing one particle-size fraction requires at least one of the other fractions to change.
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

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

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Ask students to predict the result before you change a setting. Compare the new view with the starting state.

Guide the demonstration

Read the sand, silt and clay axes and locate the selected mixture in the texture triangle. Check that its fractions add to 100%.

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

Discuss a common misconception

“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.

Build the explanation

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.

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

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

Teaching notes

Classify mineral texture using the proportions of sand, silt and clay, not the soil’s colour or a commercial label.

Check that the three mineral fractions total 100% before plotting a point on the triangle.

Explain that peat is dominated by organic material and is not a fourth corner of the mineral texture triangle.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Sand

Read the definition

Silt

Landsat view of the Thames estuary, coastal shallows and offshore wind farms. — NASA Landsat observation of the Thames estuary. The tidal river widens towards the North Sea; pale water reveals suspended material and shallow coastal water.