Chrysoprase
Wonderful things are told of the virtue of the chrysoprase, for Volmar states that, if a thief sentenced to be hanged or beheaded should place this stone in his mouth, he would immediately escape from his executioners.69 Although we are not informed in what way this fortunate result was attained, it seems likely that the stone was believed to make the thief invisible, and thus possessed a virtue often attributed to the opal.
A strange story regarding a magic stone reputed to have been worn by Alexander the Great is related by Albertus Magnus. According to this recital, Alexander, in his battles, wore a “prase” in his girdle. On his return from his Indian campaign, wishing one day to bathe in the Euphrates, he laid aside his girdle, and a serpent bit off the stone and then dropped it into the river.70 Even Albertus, who is far from critical, admits that the story seems like a fable, and it probably belongs to a comparatively late period. As the term “prase” is used very loosely by early writers, this “victory stone” may have been an emerald or possibly jade.