Zirconium-containing BaO- and PbO-free X-ray opaque glasses having a refractive index nd of about 1.54 to about 1.58 and a high X-ray opacity with an aluminum equivalent thickness of at least about 500% are provided. Such glasses are based on a SiO2—B2O3—Al2O3—R2O—RO—La2O3—ZrO2 system with optional additions of SnO2. Such glasses may be used, in particular, as dental glasses or as optical glasses.