2. Basic components: minerals


Fine mineral components

The colour of the groundmass of the soil is very varied

Red. It indicates the presence of finely dispersed Fe compounds. Sometimes they are amorphous gels and very often they are haematites.

Yellowish reddish-brown. It indicates dispersed hydrated iron compounds, goethite and lepidocrocite.

Reddish-brown to very dark reddish-brown. Generally due to organic matter.

Grey. The colour of many minerals, such as clays, feldspars and carbonates.

Green to greyish-green. Ferrous compounds (and less frequently, glauconites and clorites).


For the fine mineral components, there is a description of: nature, colour, degree of transparency (transparent, speckled, dotted, cloudy and opaque) and interference colours.


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