Detection and investigation of roméite group minerals in historical silicate glass using electron backscatter diffraction and microcathodoluminescence spectroscopy

Early 19th century silicate glass of opal beads made at Murano has been studied by means of X-ray fluorescence spectroscopy, scanning electron microscopy, energy dispersive X-ray spectral analysis and elemental mapping, electron backscatter diffraction, and cathodoluminescence spectroscopy and mapping. The studied glass has been found to contain micro crystals of some accessory minerals associated with the quartz raw material at the site of extraction; they got into the glass melt with quartz as an uncontrolled impurities during glass making. Most of these particles are minerals of the roméite group, mainly fluorcalcioroméite and “fluornatroroméite”; the glass studied also contains micro inclusions of baryte and cerussite. Micro cathodoluminescence spectra of opal glass and fluorcalcioroméite inclusions have been investigated; the spectra of fluorcalcioroméite consist of a broad high-energy band and a much narrower low-energy one at the temperature of both 300 and 80 K. A set of narrow lines with maximum close to the quantum energy of 1.7 eV are a feature of fluorcalcioroméite luminescence; these lines predominate at the temperature of 80 K in its low-energy CL band. Based on the mineral composition of the micro inclusions, possible places of mining of the quartz raw material used for the manufacture of opal beads in the 19th century have been discussed. Several locations in the territories of modern Italy, Switzerland and Austria have been considered. It is concluded that mineral particles in historical glass can be used for the provenance determination of the silica raw material used for the glass production.