Archmage's Spell book

"This must've been made by a very environmentally conscious wizard..."

This ornately designed book when found in prime condition will seem to hold only one blank page. When both sides of that page are fully used for the transcribing of spells, a new blank page will materialize for the owner to use.

The book is immune to any damage (fire, water, etc.)

When a page is torn out either,
-If the page is full with a spell, a copy of said page will appear, preserving the spell.
-If it is a partially used page, a blank copy will appear.