Figure 2

Soil Fabric Of Andosols In The Valley of Geysers. Two left rows—optical microscopy images (plane polarized light—PPL; cross polarized light—XPL; reflected light—RL; photos by M.P. Lebedeva). Right row (photos by M.S. Chernov): i—l—SEM images at two magnifications: on the left—a general view of a microaggregate, on the right—a detailed image of the surface: (a) Loose, porous, microaggregated material with fragments of deeply altered rocks and minerals, brown microaggregates (peds—1) and coprolites of soil micro- and mesofauna (2), fragments of semidecayed plant remains (3). (b) Inclusions of deeply altered rocks and minerals (4) within a subangular blocky microaggregates (1) with Fe-humus-clay microconcentrations and small coprolites of mesofauna (2). (c) microaggregates (1) of different sizes consisting of a brown collomorphic organomineral material and a finely-dispersed material that binds fragments of plagioclases (Plg), ore minerals (OM), with coatings of a collomorphic material (arrow). (d) Light-colored particles of argillized ash, with layered brownish yellow Fe-clay coatings (arrows) within intrapedal pores, singular small cracked grains of plagioclases (Plg) and ore minerals. (e) Granular, highly porous, brown material consisting of deeply altered fragments of volcanogenic minerals, assimilation of cracked sand-sized grains of plagioclases (Plg) and silt-sized grains of pyroxenes (PR). (f) A highly porous zone with rounded argillized ash particles with dark coatings and zones of iron hydroxide concentrations. (g) The uppermost part of a biogenic crust with microlayers of brown collomorphic material (brace) and yellow-white fine-crystalline material with charred particles as well as silty-collomorphic material with inclusions of silt-sized grains. (h) A red-colored zone with an intense intrusive impregnation by collomorphic Fe, with yellow altered argillized minerals and abundant charred particles and fine-silt-sized ore minerals (OM). (i) Sand- and silt-sized organomineral microaggregates consisting of volcanic glass (G) fragments (volcanic ash or tephra particles), crystals of plagioclases (Plg) and potassium feldspars (Fsp), microaggregates of clay particles and organic matter, with traces of activity of soil microorganisms and plant remains. (j) A non-oriented mass of densely packed silt–clay microaggregates consisting of kaolinite, smectite, mixed-layered clay minerals and fragments of primary volcanic minerals such as volcanic glass with intrapedal pores fully filled by newly formed (hydrothermal) minerals including pyrite, cristobalite and, presumably, zeolite (acicular crystals of zeolite minerals). (k) Kaolinite microaggregates with ‘domain-like’ microstructure in a non-oriented clay matrix. (l) A dense groundmass consisting of kaolinite and kaolinite-smectite mixed layered minerals microaggregates.