More than a mere book it is apparently a piece of ancient technology, the actual frame and protective casing acted as a conduit that could directly affect the Primal energy and agitate it into a 'raw and useable state'. The ring needed to open the book was also the actual trigger mechanism that allowed the book's 'frame' to function in this way as a completed circuit.
The "pages" of the book do have symbols and glyphson how to use the book to harness the Primal through a ritual or process.
- There are two known copies of the book. The first was delivered to Baron Northcrest and used in the initial channeling of the Primal in the prologue of the game. This one was destroyed in the ritual. The second was found in the ancient Keeper Library below the current South Quarter. This one was commissioned to be stolen by Garrett for Orion and later used to once again channel the primal. It's unknown if this version of the book was destroyed.
- The book likely holds its origin with the Keepers from the original Thief series, as it holds a similar locked design to many books depicted in the briefings of The Dark Project (locks on books such as the Compendium of Reproach were in the shape of a Glyph symbol). It contains several unidentified symbols that are implied to be glyphs. Finally, the second copy's presence in the ancient Keeper Library implies its origin.
- The gear shape itself looks similar to Mechanist banner symbol in Thief 2. However, there is no known link between the Mechanists and any mystical energies such as the Primal. The Mechanists focused far more on science and industry.
- On the other hand since its not actually a book, it may not actually be Keeper related but possibly traces back to the Precursors (the same technology that the Mechanists based their technology on), but considering its danger the Keepers would have held it to keep it out of the hands of others who would try to destroy the balance.