Petrography of Various Soils Derived from Volcanic Ejecta

Abstract

Soils derived mainly from volcanic ejecta can be recognized generally by the presence of glass particles, when such particles occur in noticeable quantity. From the data here presented, it appears that the soils examined fall into three general classes: (a) Very silicious soils containing large proportions of isotropic material of low refractive index and associated with comparatively large proportions of quartz. Illustrations are furnished by the samples from Nebraska and Kansas. (b) Soils containing isotropic material of higher refractive index, relatively large proportions of olivine, and little or no quartz. Examples are the Hawaiian soils. (c) Soils characterized by the relatively larger number of mineral species readily recognized, and especially by the occurrence of well-developed lime-soda feldspars. Examples are the samples from Washington. The presence of relatively large proportions of glasses in certain soils derived mainly from volcanic ejecta, owing to the chemical characteristics of glasses in general, suggests that, with such soils, the inorganic soil material would be more readily and quickly modified than with soils of other origin.