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Fig. 4 | Earth, Planets and Space

Fig. 4

From: Mineralogical study on volcanic ash of the eruption on September 27, 2014 at Ontake volcano, central Japan: correlation with porphyry copper systems

Fig. 4

BEI images of volcanic ash particles. a A grain consisting of coarse equant crystals of silica mineral, K-feldspar, and albite, forming equigranular texture, partly replaced by diffusively mottled chlorite and muscovite. b Colloform texture in a grain consisting of silica minerals–K-feldspar. The colloform texture consists of K-feldspar-rich bands (brighter) and a fine-grained mixture of silica mineral and K-feldspar (darker). c Grain of altered rock that belongs to the silica–K-feldspar ± albite ± garnet ± biotite assemblage in the medium fraction. The porous equigranular texture consists of tens-µm-sized equant crystals of silica mineral, K-feldspar, and albite (darker). Anhydrite crystals (bright) are attached conjugate with the grain. d The fine fraction consists of free euhedral crystals of alunite and gypsum

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