From Discworld MUD Wiki
It appears as an origami tome.
This book is made from tradition, Agatean origami. How someone was able to fold a single piece of rice paper into a book of this size, complete with seperate pages, we may never know. The face of this book is shinier than most books you've seen before. It calmly reflects your image subtly across the cover.
An octarine shimmer plays across this book slowly and hypnotically.
This book can appear in any of the four tome locations inside the library.