start wit mineralogy. William Nesse's "intro to Optical Mineralogy" is a good reference and beginners text. Its good enough to keep as a quick reerence if your a pro as well. (Ive got 2 editions nd both of them are heavily used)
Rocks, (Petrology, I think you should wait if your a beginning hobbyist or student). Theres a lot of thermodynamics and whats known as "phase rule" involved in igneous petrology and you need to understand minerals before we mix em up to make rocks).
I know there are many used copies of Nesse . If you buy his latest dition new itll cost about 130 bucks and I know that, if you search ABes or other book places that sell used books for college courses, you can get it really cheap . (Lowest I saw as abou 5 bucks for a used one, and the editions dont change drastically, they justadd minerals)
For everything but Silicate minerals the "DANA SYSTEM OF MINERLOGY" is still the best (but you should know your crystallography crap first.
NESSE's the best IMHO