NEW INSIGHTS ON THE ORIGIN OF VITRIFIED ROCKS FROM SERRA DI VUDA, ITALY

Unusual melted rocks were discovered on a hill near Serra Vuda, Italy in the Sila Massif (about 39^o 30’ 37” N, 16^o 22’ 06” E) in 1970 and an initial investigation via petrographic microscope led to the uncertain interpretation of the origin to be of meteor impact or anthropological. The purpose of this research is to do mineralogical investigation of the fused rocks of Serra Vuda to determine their origin using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The vitrified rock studied in this research was collected summer 2018. The sample was broken up and sorted into grain size <1000 µm and >500 µm by color using an optical microscope. Thin sections of the vitrified rock were observed under petrographic microscope and SEM to support our findings. XRD analyses were performed on the bulk sample, black glass sample, quartz and plagioclase sample, and black glass with a red coating. SEM imaging was used to confirm the the XRD data and to collect images on the morphology of the vitrified sample.

XRD analyses revealed that quartz and cristobalite were abundant throughout all the fractions. Albite, mullite, and cordierite were also found. Spinel was observed in the glass and red coat fractions as well as in the bulk fraction. Coesite was detected in the glass fraction only. The SEM confirmed the XRD results and energy dispersive X-ray spectroscopy (EDS) analysis identified the spinel as hercynite.

The newly formed cristobalite and coesite confirm conditions of high temperature (~ 1700 °C) and pressure (~ 2.5 GPa). Mullite and cordierite are refractory minerals indicating high thermal shock resistance (~ 1800 °C). SEM observations show that hercynite is a recrystallization product, whereas albite and quartz are remnant minerals from the target material. Planar deformation features were observed in quartz in thin section using a petrographic microscope. The XRD and SEM results suggest that the origin of the sample is from a shock impact and exclude the anthropogenic origin. Further analyses on the mineralogical and chemical features of residual minerals within the glass would be beneficial to further understand the thermodynamics within the impact system.