Alterite areas furniture - Metropolis

Areas where the presence (or absence) of loosely altered geological formations has been identified or is assumed.

In a broad sense, an altered formation is a geological formation ‘having undergone, as a result of the action of water, changes in its original chemical and mineralogical composition but also in its physical properties (mechanical, electrical, elastic, hydrogeological)’.
These alterations may be:
soustractives (exportation nette de matière sous l’effet du lessivage) aboutissant à des profils latéritiques ainsi que leur variante bauxitique sur des roches silicatées ;
additives (apport net de matière) aboutissant à des précipitations formant des encroûtements de type silcrètes, calcrètes...

The area mapped here is limited to the ‘saprolite’, a generally clay-dominated movable horizon forming the upper part of a lateritic profile developed on metamorphic, plutonic or volcanic rocks. We are therefore only interested in alteration in its subtractive form and in the basement context only within the meaning of the BDLISA framework, namely within magmatic and metamorphic geological formations.

(According to Sandre, dictionary of the SAQ V 2.2 hydrogeological repository)