A quartz glass provides an opaque quartz glass having high light-shielding property, excellent mechanical strength and excellent cleaning resistance against hydrofluoric acid. By setting the maximum width of the amorphous bubbles existing in the opaque quartz glass to an average of 3 to 15 μm and the density to 2.15 g/cm3 or more, the mechanical strength after baking and the cleaning resistance by hydrofluoric acid are improved. The opaque quartz glass has a whiteness at a thickness of 10 mm of 75 to 90%, the reflectance of light with a wavelength of 0.24 to 2.6 μm at a thickness of 4 mm is 60 to 85%, and the bending strength after baking is 95 MPa. In addition, a foaming agent may be mixed in the opaque quartz glass. An opaque quartz glass having cleaning resistance against acid can be obtained.