Secondary iron compounds are the foremost coloring agents in subtropical and tropical saprolites. Amorphous Fe(OH)3 and goethite are yellow in submicron particles, and coarse goethite is brown. Submicron hematite is red, whereas coarse hematite is gray to black. At most outcrops the color of saprolite is due to the secondary ferric compounds: the hue of the color relates to the mineralogy and particle size of the ferric pigments; value and chroma vary systematically with the proportion of pigment.
The color of the saprolite determined by visual comparison with a Munsell Soil Color Chart and referred to our diagram yields a rapid estimate of total iron, as well as ancillary information about particle size and hydration state of the ferric compounds.
- Geological Society of America