Christopher DuffinLondon, England Gemstones such as sapphire, ruby, emerald, and topaz are complex silicate minerals. Their distinctive and intense colors, hardness, durability, and rarity suggested medicinal value to medieval scholars, famously summarized in medieval lapidary texts, or books about such stones. In the early 15th century, Monsieur Chiquart, Master Chef to the Duke of Savoy,…