Clays are the result of the hydration of feldspar* from granitic rock.
It’s a sedimentary rock composed mainly of hydrated aluminium silicate.
* Feldspar is the most important group of minerals in the earth’s crust.
Chlorite can colour the clay green.
Manganese, magnesium, copper… all metals can colour clay, but especially iron:
Fe+ = yellow clay
Fe++ = red clay
Fe – = green clay
The yellow and red clays come respectively from an increasingly active exposure to air (Fe+, Fe++).
The green clay comes from its formation in the absence of air (Fe -).
Colour is not synonymous with efficiency: for example Montmorillonite, which is a very active clay, can be yellow, pink, green, etc.
There are several types of clay:
These clays have an ADsorbent or ABsorbent (depending on types) capacity.
Clay is a material endowed with the intelligence of Nature and therefore favourable to life: it fixes by ADsorption what is contrary to it and it gives what is favourable to it by a phenomenon of ion exchange (Smectites and Bentonites) or by ABsorption, i. e. like a sponge (Illites).
o Kaolin: white clay of Kao Ling, in China
o Illite: more common clay, also known as “pottery clay”.