Greek Gold: Jewelry of the Classical World
Photoatlas of Inclusions in Gemstones, Vol. 1
Ruby & Sapphire Though I own a more recent edition, Richard Hughes remains a foremost expert in the field of corundum. Highly recommended reading!
Beyond Extravagance: Gems and Jewels of Royal India (Legends)
Boucheron: The Secret Archives
London's Lost Jewels: The Cheapside Hoard