Opals
by Fred Ward

Gemmological Association of Australia says:
Beautifully photographed...researched with Ward's usual thoroughness...easily understood.

Opal Cutting Made Easy

by Paul B. Downing

The title says it all. Anyone that owns this book can cut a fabulous opal. Information for identifying which way to cut, how to treat and maintain the best fire. Comprehensive charts for sanding grits and polishes. Guidelines for thickness of opals of various sizes. He scoffs at the horror stories and makes identifing and cutting opals so simple

Opal Identification & Value
by Paul B. Downing

Learn to properly identify opals from all over the world. Many new locations have been added along with new methodology to determine the characteristics that affect value, then determine price from updated value tables. Ascertain if the opal is a natural solid, boulder, doublet, triplet, dyed or lab-created.

Opal: Advanced Cutting & Setting
by Paul B. Downing

Containing 33 color and 104 black & white photos and diagrams, Paul Downing has condensed his 30 plus years of experience in opal cutting and jewelry design into simple, easy to understand instructions

Gemstone Buying Guide: A Guide to Buying
by Renee Newman, GG

Although, not specifically about opals, this book has a stellar section on them!