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Earth, Planets and Space
Fig. 3 | Earth, Planets and Space

Fig. 3

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

Fig. 3

BEI images of volcanic ash particles. a Typical partly altered volcanic fragments in the coarse fraction containing microlites of plagioclase, anorthoclase, sanidine, and minor interstitial glass. Some of plagioclase microlites and glass were replaced by pyrite, silica mineral, kaolin-group mineral, and muscovite. b The silica–pyrite assemblage in a grain containing darker pseudomorph in the matrix. Pyroxene phenocryst is replaced by silica mineral, and pyrite crystals fill the cleavage of the pseudomorphs. c The right side of the grain partly retained the original vesicular texture, while the left part shows a completely deformed texture. Narrow veinlets of vug and pyrite crystals are recognized in the deformed part (arrow). d Grains containing silica–pyrite assemblage with colloform texture consisting of micron-width wavy bright bands and darker matrix. e Grain consisting of silica mineral, pyrite, alunite, kaolin-group mineral, showing pseudomorphic volcanic texture. Original crystals were replaced by silica mineral or kaolin (darker) or became void. f A silica minerals–pyrophyllite–pyrite assemblage grain comprises anhedral silica crystals (gray) and a fine-grained matrix of pyrophyllite (darker)

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