Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

Research on obsidian lavas from Lipari and Vulcano in the Aeolian Islands reveals that spherulite formation is driven by distinct processes occurring at different cooling stages, leading to significant heterogeneity in size, shape, and composition. Spherulites, ranging from <1 mm to 8 mm, exhibit radial interiors and can occur individually or within deformation bands, sometimes surrounded by clear haloes and brown rims. Their mineral content includes cristobalite (α, β), orthoclase, titanomagnetite, and rhyolitic glass, with growth periods averaging 5 days and potential modification over hundreds of years at lower temperatures. Crystal Size Distribution (CSD) analysis shows varying size populations and growth rates, while elongation in high-temperature spherulites triggers further nucleation and growth. Spherical forms dominate mid-glass transition temperatures, and vapor-phase modifications occur at lower temperatures. Enhanced undercooling, deformation, and modification play pivotal roles in shaping spherulite diversity in these volcanic rocks.

Liam A., Bullock, Ralf, Gertisser, & Brian, O’Driscoll. (2017). Spherulite formation in obsidian lavas in the Aeolian Islands, Italy [JB]. Periodico di Mineralogia, 86(1). https://doi.org/10.2451/2017PM680