"A Tome of Mystic Secrets for Fantasy Roleplaying"
As massive an expansion GURPS Basic Set Third Edition represented over the previous basic sets, GURPS Magic was a similar expansion over the original GURPS Fantasy. 112 pages.
Released in early 1989 with parts incorporated into the second and later printings of GURPS Basic Set Third Edition, GURPS Magic cleaned up the Magic rules, added over 100 new spells, a new college, rules for improvised spells, new advantages and disadvantages, new magical creatures and a host of other magical odds and ends.
There were two very different covers for GURPS Magic, but the contents were the same (other than a few typos corrected).
Went through three printings.