Chroma
Definition
The saturation or colourfulness of the hue, from 0 (neutral grey) outward in whole-number steps. Strongly weathered, iron-oxide-rich soils have high chroma; gleyed (waterlogged, reducing) soils have near-zero chroma.
- Chroma range
- 0 (neutral grey) to 8 (vivid); whole-number steps
- Gleyed soil chroma
- 0-2 (low saturation from waterlogging)
- Laterite soil chroma
- 6-8 (high saturation from iron oxide)
Common questions
What does chroma mean in soil forensics?+
Chroma is the saturation or colorfulness of soil hue measured on the Munsell scale. It ranges from 0 (neutral grey) to 8 (vivid), with higher numbers indicating more vivid, saturated color. Forensic examiners use chroma alongside hue and value to create a complete soil color profile.
How does chroma tell you about soil conditions?+
Chroma values reveal soil chemistry and water history. Iron-oxide-rich, strongly weathered soils have high chroma (6-8), while waterlogged or gleyed soils have near-zero chroma (0-2) because reducing conditions bleach the color. Comparing chroma between soil layers can show whether a site was recently disturbed or moved.
Why use Munsell chroma instead of just saying red or brown?+
Munsell chroma standardizes color so different examiners describe the same soil identically. A soil described as chroma 2 will look the same to anyone using the Munsell system, making comparisons reliable in casework and court testimony.
Related terms
- Hue
- The dominant wavelength family of a colour, expressed as a position on the Munsell colour wheel. Soil hues run from 10R (red)...
- Value
- The lightness dimension of the Munsell system, scaled from 0 (theoretical black) to 10 (theoretical white). High-organic soils tend to have low...
- A Horizon
- The uppermost mineral soil horizon, darkened by organic matter accumulation and the layer most commonly transferred by footwear and vehicle contact.
- Clay Mineral
- A secondary phyllosilicate mineral produced by chemical weathering; includes kaolinite, illite, smectite, and chlorite, all diagnostic of parent material and weathering intensity.
- Inter-Observer Variability
- The tendency of different trained examiners to assign slightly different Munsell codes to the same sample. Research has shown this can span...
- Loss on Ignition (LOI)
- Weight loss after heating dried soil to 550 degrees Celsius. Approximates the organic matter content. A simple, cheap, high-yield discriminator in field...
- Munsell Chip Comparison
- The visual procedure of matching a soil sample against printed colour chips in the Munsell Soil Colour Chart under standard daylight conditions,...
- Munsell Notation
- A three-component colour code (Hue-Value/Chroma) standardised under ASTM D1535 for describing soil colour from the Munsell Soil Colour Chart.
- Munsell Soil Colour Chart
- A physical book of matt colour chips arranged by hue, value, and chroma, published by X-Rite/Munsell Color. The analyst holds a chip...
- Particle-Size Distribution
- The quantitative measurement of the proportions of gravel, sand, silt, and clay in a soil sample, determined by sieving and hydrometer or...
- Soil Texture
- The relative proportions of sand, silt, and clay in the mineral fraction of a soil, expressed as a USDA or ISSS texture...
- Spectrophotometry
- Instrumental measurement of reflectance at each wavelength across the visible spectrum, producing a numerical colour profile. Results can be expressed in CIE...
Explained in these topics
- Soil Colour and Munsell NotationThe saturation or colourfulness of the hue, from 0 (neutral grey) outward in whole-number steps. Strongly weathered, iron-oxide-rich soils have high chroma; gl...
- Soil Composition, Classification and the Munsell SystemThe saturation or purity of colour in Munsell notation, from 0 (grey) to 8 (vivid); gleyed soils have chroma 0-2 and bright laterites can reach 6-8.