There is no "X" to close the book on my screen. Compared to the OP:

IMHO, ESC should close the book. I tried several keys but could find no way to close it via the keyboard.
Win 7 64-bit
Nvidia GeForce 310M (notebook) - latest manufacturer drivers (via Samsung)
1366x768 (full-screen or windowed)
DxDiag: http://pastebin.com/SUWc7cwD
EDIT: The game appears to be defaulting this notebook to a lower graphic setting. In this setting, the "X" to close the book is missing. I tried running Elemental on my desktop (1680x1050) and was able to see the "X" on that machine (the menus also showed more graphical detail vs. the simplified menus shown on the 1366x768 notebook screen).