if its not stamped its likely NOT silver or gold. All sterling is stamped 925 and a lot of silver coming out of mexico and south america are now being stamped 945 or even slightly higher. if its not stamped, its not sterling. same goes for gold. in canada. anything below 10k is not legally allowed to be called gold, so it could be that its 8 or 9k gold and that means 8 or 9 out of 24 parts gold (meaning so little gold in it its pretty much NOT gold)
and are you sure its not a cz? how do you KNOW its a diamond?