There was a time when these kinds of exquisitely beautiful stone images graced many of these places. A similar example, though without a mirror, can be found in the cloister of the Monastery of Santo Domingo de Silos. One could say that these, like the plays of light, were part of the 'special effects' of the era. The altarpiece containing this image is also monumental and solid enough to support such weight. Thank you very much for your comment and best regards.