Disclaimer: Some links on this pager are Amazon Affiliate links and as such, I earn from qualifying purchases. The books here are books that I can personally recommend and have either referenced in blog posts or used in the past for coursework.
General
The historian Lecouteux has put together what amounts to a dictionary of stones and gems. It is extensively researched and pulls from a number of ancient sources, though the names used often aren't the colloquial names for the stones.
Christianity
Ehrman and Plese have put together a collection of the apocryphal Gospels, including the fragments, in a single volume set
Renowned scholar Bruce Metzger's work examining the development of New Testament canon
Malleus Maleficarum
By the same editor who created the two-volume set below, this is an English translation of the Malleus Maleficarum
Malleus Maleficarum is a weird book that didn't necessarily reflect any common views of its time period and as such can be hard to understand. This book examines the Malleus Maleficarum in its medieval context and explains the twisted perspective it's working from.