Gempedia: A Comprehensive Glossary for Gemstones and Gemmology is a friendly & useful reference book. We say “friendly” because while it’s substantial indeed (over 7,300 entries), it’s also easy to hold in one hand while flipping through the pages, and has good-sized print and nice margins. Entries include trade names, organization names, technical terms, and more. There is a section at the back for numerical entries, and a final short section for symbols.
This book is text-only. It is not a coffee-table picture book. It is, however, a good companion to all of those coffee-table books, as it can provide one with definitions and context for all the unfamiliar words in their captions and blurbs. It would also make an excellent gift.