Pyroxene inclusions in paleo-Christian mosaic tesserae: a new tool for constraining the glass manufacturing temperature

摘要

The mineral inclusions of two orange glass tesserae from paleo-Christian mosaics were investigated in order to derive the melting temperature reached during their production (sourced from Padua and Vicenza, Veneto region, Italy). In particular, clinopyroxene crystals were studied by single-crystal X-ray diffraction and electron microprobe WDS analysis. The crystals show C2/c symmetry, typical of disordered Ca/Na and Mg/Al distributions indicating high-temperature of formation (>700°C). The cation site populations were obtained by combining results from the two experimental techniques enabled us to derive the following stoichiometric formula: lM2[Ca_0.819Na_0.172Mn_0.006K_0.003]M1[Mg_0.765Fe3+_0.210 Cu_0.015Ti_0.006Zn_0.006]T[Si_1.933Al_0.037Sn_0.024]O₆begin{array}{l}{}^{M2}[mathrm{Ca}_{0.819}mathrm{Na}_{0.172}mathrm{Mn}_{0.006}mathrm{K}_{0.003}]{}^{M1}[mathrm{Mg}_{0.765}mathrm{Fe}^{3+}_{0.210}[3pt]quad{}mathrm{Cu}_{0.015}mathrm{Ti}_{0.006}mathrm{Zn}_{0.006}]{}^{T}[mathrm{Si}_{1.933}mathrm{Al}_{0.037}mathrm{Sn}_{0.024}]mathrm{O}_{6}end{array}