What is my birthstone?

I was born in October, and I've always considered my birthstone Rose Zircon, and known that Opal was an alternate birthstone, but double-checking what it was to tell my girlfriend, I can't seem to find Rose Zircon in any of the official listings of birthstones, and instead find out that Aquamarine and Tourmaline are also alternate stones. (She got me a necklace with a Tourmaline stone in it, and I was confused, but I couldn't exactly remember what my birthstone was, aside from the fact that it was pink.)