Nanoscale inclusions in magnetite

Magnetite from the El Laco volcano, Chile, is controversial in terms of its genesis.

A magmatic model is proposed from structural features explained by melt immiscibility, whilst a hydrothermal model is suggested from geochemistry associated with ‘flotation theory.’ Magnetite was studied at micron- and nanoscale using samples from lava-flows and steam-heated products.

This research was carried out using advanced electron microscopy techniques, including scanning transmission electron microscopy. Results show that magnetite displays oscillatory-growth defined by sub-micron-sized silicate inclusions.

These are identified as Ca- and Mg/Fe-rich pyroxenes, known as augite-pigeonite pairs. STEM imaging reveals atomic-scale intergrowths with abrupt terminations of one pyroxene into another, typical of fast-growth during lava cooling, convincing evidence for a magmatic origin. Sulphur-bearing phases coating magnetite from steam-heated products suggests sublimation from vapours along degassing tubes, interpreted as evidence for magnetite transport in suspension.

Theme
Future energy and resources

Booth
FE27

School
Chemical Engineering and Advanced Materials

Exhibitor
Stuart Andrew Heap

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