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.
Future energy and resources
Chemical Engineering and Advanced Materials
Stuart Andrew Heap