Could someone explain to me exactly what an agate is? Do they always have to be transparent? I know they come in different colors (rootbeer, amber, clear, etc)... we have a large amount of them where I live, a little more info on them would be great!

Do a Google (or Yahoo or... ) search on "agate" and you will get more info that you know what to do with.

Also, check you public library or a University library. There should be a book or two on agates in any library.