Allophanes occurrence

According to Sudo [1963], one of the important occurrences is in the Kanto volcanic ash soils. The principal clay minerals are (meta) halloysite, hydrated halloysite, and allophane. Randomly interstratified halloysite-hydrated halloysite occurs in the lower horizons and gives a basal reflection consisting of a broad band sometimes or 7 A reflection tailed toward lower angles. 

The occurrence of allophane in rocks is associated with conditions that favor formation of random-structure aluminosilicates. Thus, allophanes of geological origin that occur in fissures of ore veins, on linings of cavities in marl, and in similar locations, appear to have been formed by precipitation at relatively low temperatures and pressures from solutions containing silicon and aluminum. Hydrous aluminosilicates prepared artificially in a similar... 

The occurrence of allophane in soils is favored by conditions that lead to the formation and persistence of random structures. 

Kanno [1964] described the occurrence of allophane in a humic allophane soil from the Tachikawa loam bed of a soil in Mitaka, Tokyo, derived from basaltic ash. Similarly, the amorphous clays from certain soils from basalt of northern Ireland and many other parts of the world are allophanic, and the amorphous clays in young soils derived from ultrabasic rocks such as dunite in New Zealand clearly have allophanic constituents, though these may be inseparable from gels of hydrous iron oxides, antigorites, and other secondary minerals. 

---