The phrase "gem of a book" is an idiomatic expression that means a book that is exceptionally good, valuable or worthy. It implies that the book is a treasure or something truly special and it's worth reading or owning.
Sentences with «gem of a book»
This little gem of a book for teachers will provide lots of laughs, as well as many insights into the nature, quirks, and vulnerabilities of gifted, talented, creative kids. (greatpotentialpress.com)
Of course, there is a written history of the console, but the real gem of the book is the pictures. (the-gamers-lounge.com)
Last week, I stayed up until 3 a.m. reading this absolute gem of a book. (thecuriouslemon.com)