I don’t really have a lot to go on, but when I was in 6th grade (so around `94) I read this scifi book my teacher had and literally all I can remember is they travelled from at least one planet to another, and there was something to do with a green stone and it may or may not have given the heroine special abilities. I’ve been trying to search for it for years, as I believe this may have been one of the catalysts for my interest in the scifi genre. Suggestions: The Edge Chronicles by Paul Stewart and Chris Riddell, Forerunner Foray or The Zero Stone, both by Andre Norton.
Lost Classics of Teen Lit: Name That Book! 