Textural Triangle
Definition
A ternary diagram with sand, silt, and clay at the three apices. A point plotted from the measured percentages of those three fractions falls within a named texture class. The USDA and ISSS systems use different size boundaries, so the same sample can fall in different classes depending on which system is applied.
- Apices
- Sand, silt, clay
- Systems used
- USDA and ISSS
- Basis
- Measured percentage of each size fraction
- Field
- Particle size and soil texture analysis
Common questions
Why does the same soil sample fall into different classes under different systems?+
USDA and ISSS define the sand, silt and clay size boundaries differently, so a fraction counted as silt under one system may fall into the sand or clay range under the other, shifting where the same sample plots on the triangle.
Why is texture classification useful in forensic soil work?+
A soil's texture class is a quick, reproducible way to compare a questioned sample against a reference location, and consistent classification protocols let examiners in different labs communicate results on common terms.
Related terms
- Hydrometer Method
- A sedimentation technique that uses Stokes' Law to determine the proportion of silt and clay from the rate at which particles settle...
- Laser Diffraction
- An instrumental method where a dispersed sample passes through a laser beam and the angular diffraction pattern is inverted to produce a...
- Particle-Size Distribution (PSD)
- The proportion by mass of soil particles falling within each size fraction. Expressed as a curve or a table of percentages, and...
- Ribbon Test
- A field method for estimating texture by wetting a small amount of soil and extruding it between thumb and finger. The length...
- Sieve Analysis
- Mechanical separation of soil particles by passing a dried, dispersed sample through a stack of sieves with calibrated apertures from 2 mm...