Check out what your local university or college has listed for their physical geology text book(s), visit their book store and see if they fit the bill. A very useful book for identification, surprisingly, can be in the form of a lab book as well. If those are too costly, perhaps they would make a good future investment or you can find them online as pdf's, or e-books. In the mean time, there are also plenty of field guides, for example that may interest you, or even that you can print out (pdf) for basic identification.