Emerald was worn to guard against plague, falling sickness, and venomous bites. As with other blue and green gems, it was considered to be an eye stone, and bathing the eyes with water in which this stone had soaked for six hours would cure most ailments, as was the case with aquamarine. Some believed if it was held in the mouth, hemorrhaging would cease. If it was placed on the belly and in the mouth, dysentery would disappear. Bound to a woman's thigh, emerald was thought to ease childbirth. It was also mentioned to cure leprosy.

King Arthur's "San Graal" was carved from a large emerald, and thus the gem became a symbol of chastity. In fact, it was believed that this pristine gem would break apart in the presence of lust, so its wearers were forced to choose between it and their passions. It was believed to reveal adultery, since it was believed to grow dark when a lover was faithless.

One mystical power attributed to emerald is the ability to foretell the future, if the stone was placed under the tongue. Some thought if a serpent gazed upon an emerald, it would be blinded. Emerald was sometimes given to "possessed" people (suffering from epilepsy or asthma) to exorcise the evil spirits. Another myth was concerning creation, that emerald was created white and turned green after ripening. Emerald supposed to be set in gold for maximum potency.