Marbod of Rennes: De Lapidum Naturis

This short prose lapidary is printed with the works of Marbod of Rennes, alongside his verse book on gems, though its connection with him is uncertain. It lists the virtues attributed to various stones when worn or carried. Jasper protects against lightning and thunder; chalcedony, consecrated and bound on, cures lunatics and preserves its bearer from drowning, and should be engraved with an armed Mars or a robed virgin holding laurel.

An emerald hung at the neck or worn on the finger is said, on the authority of a book on stones ascribed to Aristotle, to protect against epilepsy, and the text advises nobles to hang it on their children’s necks. Other entries concern dreams, sorcery, conception and childbirth. The text belongs to the practical, magical side of medieval stone lore, and it shows how such beliefs were transmitted alongside the more literary lapidaries.