ABSTRACT

Crystallization ƒ There are two stages in the crystallization of mineral substances: • Germination, also called nucleation, • Crystal growth. In a dilute medium, for example in a jar with a substance in solution, seeds rarely appear; they mark the prior joining of some ions. Crystals will thus be few but develop without difficulty. But in a soil, impurities capable of initiating crystallization are infinite in number. In these conditions, germination takes place all over. Crystal growth can produce only small overlapping crystals that interfere with one another. In short, the soil is a medium favourable only for structures with short-range order. With time and under the influence of alternate phases of wetting and drying, the amorphous materials (in the broad sense) are transformed to well-crystallized species. This is Ostwald ripening.