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That will really have to come down to your GM. Spell books are not normally a part of the system, so the books you are dealing with aren't something we have rules for.
There was a Rifter article suggesting a sub-school of magic using them, but those were tied to the mage such that lending them out would be hazardous to their health.

Outside of that, most books with spells in them would be research materials describing spell theory and such required to understand and believe in a spell so as to learn it. Which would mostly be a matter of time and some lore and writing skill checks to create.

One of the Rifters has spellbook info in it. Not sure which one ATM.

There are also several references given throughout the various Nightbane supplements of spells in written form, but no rules are given for spellbooks.