We will now proceed to speak of the various kinds of precious stones, the existence of which is generally admitted, beginning with those which are the most highly esteemed. Nor shall we content ourselves with doing this only; but, with the view of consulting the general welfare of mankind, we shall also refute the infamous lies that have been promulgated by the magicians: for it is with reference to precious stones, more particularly, that they have circulated most of their fabulous stories, stepping, under that most alluring guise of ascertaining remedial virtues, beyond all bounds, and entering the region of the marvellous.