Inherited minerals (more or less transformed from the original material) predominate in soils. These minerals have been useful in genetic studies of soils with regard to the following guidelines:

Extending knowledge of the parent rock

Lithological discontinuities and buried palaeosols

Origin of minerals, development and nature of the alterations

Nature and degree of the alterations

Extending knowledge of the parent rock

Sand mineralogy reflects the mineralogy of the original material (rock or sediment) that the soil comes from.

This relation materialises in a series of aspects, for example:

Polymineralic grains directly conserving the mineralogy and the microstructure of the rock.

Monomineralic grains indicating a specific petrological origin. For example, quartz grains with features of precise origins (KRYNINE, 1946):

• volcanic (monocrystalline, idiomorphic, hexagonal, bipyramidal, without developed prismatic faces, without undulose extinction and with presence of corrosions),
• metamorphic (very polycrystalline, with sutured boundaries between the individual crystals, elongated, orientated, with presence of orientated mica flakes and with a strong undulose extinction),
• sedimentary (spherical and elliptical shapes, rounded boundaries and with secondary regrowths.

Minerals that would go unnoticed in the parent rock as they are found in very scarce quantities and which concentrate in the soil in this fraction. This is the case of the majority of the heavy minerals: haematite, goethite, maghemite, tourmaline, garnet, andalusite, disthene and staurolite.
Finally, we think it is interesting to note that the contribution of coarse sands to the knowledge of the original material can be extremely interesting in those cases in which there are certain limits to directly accessing the original material, such as the case of very deep soils (for example, very evolved soils, extremely thick soils with calcic horizons, etc.) or, on the contrary, soils formed on thin surface deposits with all their horizons intensely weathered and therefore without the primitive features of the original material being conserved.