The third book of Speculum Lapidum was first published in Venice in 1502 by the astrologer and doctor Camillo Leonardi, a native of Pesaro with a doctorate from the famous University of Padua. As a courtier of Costanzo Sforza when the city of Pesaro passed to Borgia, Leonardi tried to win their favor by dedicating his work to the Duke of Valentinois, Cesare Borgia, son of Pope Alexander VI.In three books, the treatise describes the nature of stones and represents a synthesis of ancient and medieval knowledge on the topic. The first two books examine the origin and classification of stones and gems; in the third book Leonardi examines their magical virtues and powers in detail. These powers are not inherent in stones, but derive directly from the sky, planets, constellations, and fixed stars. Every object, animal, herb, stone resonates with the same energy it receives from stars, and for those who are familiar with the chain of correspondences between macrocosm and microcosm, anything is possible.The book summarized the most important and well-known medieval lapidaries of its time, and thus it experienced immense good fortune. It was reprinted several times, translated into Italian, and published in 1565 by Lodovico Dolce in 1565), partly in English (in 1750), and French (Claude Lecouteux, 2002). However, the third book, owing likely to its overtly magical nature, has never been translated into English before. The third book is comprised of 19 chapters. The first chapters (1-7) are dedicated to the discussion of the nature of stones and classification of seals in terms of three aspects: universal (not depending on the material used: the zodiacal seals), particular (depending on stars' configuration: seals of stars and constellations), and significative (intensifying the inner virtues of stones: non-zodiacal/magical seals). Chapters 8-10 describe the astrological triplicities and their virtues. The remaining chapters collect several medieval lapidaries.With this translation from Margherita Fiorello, we have the opportunity to keep in our bookshelves a tome that until now was known only to the greatest experts on the history of medieval and renaissance magic, a book originally written for one Cesare Borgia, a man whose name is deeply linked with necromancy and black magic. We don't know if Leonardi believed in this legend, or if he merely intended to create a talismanic encyclopedia for his patron based on the medieval idea that stones, more than other na