Spherulites in obsidian lavas of Lipari and Vulcano (Italy) are characterisedby spatial, textural and geochemical variations, formed by different processes.Spherulites vary in size from <1 mm to 8 mm, are spherical to elongate inshape, and show variable radial interiors. Spherulites occur individually or indeformation bands, and some are surrounded by clear haloes and brown rims.Spherulites typically contain cristobalite (α, β) and orthoclase, and rhyoliticglass, and grew over an average period of 5 days, with modification at lowertemperatures. Heterogeneity relates to formation processes of spherulite‘types’ at different stages of cooling and emplacement. Distinct populationsconcentrate within deformation structures, with variations in shape andinternal structure. Crystal Size Distribution (CSD) plots show differing sizepopulations and growth periods. Spherulites which formed at high temperaturesshow elongation, where deformation triggered further spherulite nucleationand growth. Spherulites formed at mid-glass transition temperatures arespherical, and spherulites are modified at vapour-phase temperatures. Enhanced undercooling, deformation, and modification are therefore pivotal in thedevelopment spherulite heterogeneity in obsidian lavas.
- Aeolian Islands
- Glass Transition