Using balances effi ciently

Amazing Race Balance Challenge

are in a foreign country where balances are still used in the marketplace to sort out the valuable gems from the worthless stones. As a part of this challenge, we are given 9 stones and we have to figure out which stone is really the valuable gem. We are told that although they all look the same, the valuable gem is slightly heavier than a worthless stone, and that the 8 worthless stones we are given all weigh the exact same. If we use the balance more than 2 times, we are penalized and have to take 1 hour off of our travel time. That would cause us to lose the game since this is a very close race. We are determined to figure out a way to identify the stone without using the scale more than 2 times. Please help. Explain how we can identify which is the valuable gem using it only 2 times.

In Amazing Race, my partner and I