The Zohar

in Hebrew, written by Moses de Leon, 1280

This dense text is a basic text for the kabala, and contains many secrets of Jewish mysticism. It describes in great detail the division of the universe into ten spheres or sephiroth, the third of which shattered when infused with divine essence. Many of the secrets of gematria (Jewish numerology) are also made plain. The work was part of the original Orne bequest of 1765. (Johnson, Sam, and Sandy Antunes. "Miskatonic University: A Handbook to the Pride of Arkham." Chaosium, Oct. 2005.)