ABSTRACT
Synthesis ƒ The principal minerals presented form a broad, more or less continuous assemblage. Let us start from the structure of allophane and postulate, without prejudging the mechanisms: • if the tube is elongated, it is becoming imogolite, • if it is folded longitudinally and finally opens up completely to
give a plane body, it is becoming a true clay mineral, • if water is expelled from it, it is halloysite becoming kaolinite, • if iron replaces aluminium, it is going from an aluminous clay
mineral of kaolinite type to a ferriferous clay mineral of hisingerite type,
• if the proportion of silica is variable, that is, if tetrahedra are added or lost, it is alternating between 1/1 clay minerals and 2/1 clay minerals.
