When and how Fe-oxide nanocrystals form: Insights from in situ FESEM and implications for eruption dynamics

MUJIN Mayumi

Department of Earth and Planetary Sciences

Jul. 14, 2026

図1. （左）天然の火山噴出物中（霧島火山新燃岳2011年噴火）に観察されるナノ結晶の電子顕微鏡像（反射電子像）と、その均質な火山ガラスに見える場所（□）を拡大したもの（右）。ナノ結晶（明るい粒々）が晶出していることがわかる。輝度の違いは化学組成の違いを示し、種類の異なる鉱物が含まれていることを示す。

Joint press release (in Japanese) by Tohoku University and Hokkaido University

Abstract
Nanocrystals (nanolites and ultrananolites) in volcanic rocks have attracted considerable attention owing to their potential role in increasing magma viscosity and serving as heterogeneous nucleation sites for bubbles, thereby influencing eruption styles. However, the conditions, time scales, and mechanisms of their formation remain poorly constrained. In this study, we conducted high-temperature, in situ observations of crystallization in a rhyolitic silicate melt using field-emission scanning electron microscopy. Nucleation of fine-grained Fe-oxide crystals (≤100 nm in width and diameter) occurred at high number densities (∼1020−1021 m−3) under sub-solidus and oxidizing conditions, whereas their growth….

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Article Information:
When and how Fe-oxide nanocrystals form: Insights from in situ FESEM and implications for eruption dynamics, Mayumi Mujin and Michihiko Nakamura, Geology, 2026
DOI: 10.1130/G54466.1