Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

Liam A. Bullock (Corresponding Author), Ralf Gertisser, Brian O’Driscoll

Research output: Contribution to journalArticle

5 Citations (Scopus)
6 Downloads (Pure)

Abstract

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.
Original languageEnglish
Pages (from-to)37-54
Number of pages18
JournalPeriodico di Mineralogia
Volume86
Early online dateFeb 2017
DOIs
Publication statusPublished - 2017

Keywords

  • Spherulites
  • obsidian
  • Aeolian Islands
  • Glass Transition
  • Lipari
  • Vulcano

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