Commentary Purg XXXI 115-117

The four virtues prepare Dante to do something that will become, very quickly, the standard way of learning for the protagonist in this new Beatricean realm of the poem: gaze into her mirroring eyes.  As Bosco/Reggio (DDP Bosco.Purg.XXXI.115-117) explain, 'In medieval lapidaries the emerald symbolized, in addition to chastity, justice.  Further, in a passage of Brunetto Latini's Tresor (III.xiii.16), Dante's direct source, green eyes (of an emerald color) were considered an attribute of feminine beauty.  It should be added, finally, that the emerald functioned as a mirror, and the eyes of Beatrice will be compared precisely to a mirror ([Purg XXXI 119-122]).  This new interpretation has been put forward by V. Bertolucci Pizzorusso, in Studi mediolatini e volgari 17 (1969).'