The X-ray opaque glass is characterized by a composition, in mol %, of SiO.sub.2, 75-98; Yb.sub.2O.sub.3, 0.1 to 40; and ZrO.sub.2, 0 to 40. Preferred embodiments of the glass are free of Al.sub.2O.sub.3 and B.sub.2O.sub.3. The glass is produced from the glass batch by melting at a temperature of at least 1500.degree. C. in an iridium or iridium alloy vessel with the assistance of high-frequency radiation. In preferred embodiments of the glass production process at least one raw material ingredient is present in the batch as a nanoscale powder. The glass is useful in dental applications, optical applications, and biomedical applications, or for photovoltaics, or as a target material in PVD processes.