Fig. 3: Textural and petrological characterisation of fragmented clasts.
From: Nanoscale silicate melt textures determine volcanic ash surface chemistry
SEM-BSE image (a) and overlain QEMSCAN phase map (b) for polished clasts from a crushed block, with phases given in the key. c SEM-BSE image showing high-magnification matrix texture, including euhedral plagioclase feldspar (Pl) and pyroxene microlites (PxM) hosted in a glass matrix (mGl) containing numerous rounded, nm-scale bright features that may represent Fe-rich nanolites or immiscible globules. This phase is absent in a ~1 μm thick zone surrounding pyroxene microlites marked by a dashed line; the zone has decreasing BSE intensity toward the crystal surface, suggesting a compositional boundary-layer depleted in Fe relative to the matrix glass. d SEM-BSE image of the matrix in a natural volcanic ash particle from the August 2006 eruption of Tungurahua, showing the same nanoscale textural features described in (c). e SEM-SE image of the unpolished surface of an ash grain from the August 2006 eruption of Tungurahua showing bright nanoscale speckles. SEM-EDX analysis (f, g) with dashed box showing area in (e) shows that the speckles are enriched in Fe (f) and Mg (g).
