Diamonds and Gold are traded against the letter of the law but it is OK

I asked someone at work, how come if Attland's Book of Laws says that "no stone or earth is to be taken out of the land", the trade in gold and diamonds is allowed to break the law?

I was pointed to the Queen's opinion and ruling that gold and diamond are not a precious gem that is exclusive to Attland, and, furthermore, considering the trade imbalance, the equal or higher amount of gold and diamonds may be entering the country, negating the possibility of the depletion of riches that the law was written to prevent.