On their own, they have no value. They cannot be sold, and must be stored in your shelf if you want to take it out of your inventory. Once you collect all 9 of them, their true potential is revealed.
There are 9 jewels total. All 9 must be completed to assemble the Gem of Truth. Here is a list of where to find all 9 jewels:
- Examine the roof your doghouse.
- Examine the water trough in the barn where your horse is kept.
- Obtain 1,000 medals at the Horse Races. The jewel is a prize available for a 1,000 medal price. Remember that medals carry over to the next season's horse race.
- Won has a jewel available for purchase for 50,000G.
- Examine the lamp posts in between the Church and Rose Square. It can be any time of the day/night.
- Go to the second floor of the library. It will be in the southern most bookcase, if you examine the set of books furthest to your right.
- You must own the Town Villa. It can be built by talking to Gotz after collecting the right amount of material. Play the New Years Gameshow on the TV while inside the cottage and win to gain a jewel.
- You must own the Mountain Cottage, which is gifted to you by your spouse after 50 years of marriage. Examine the calendar in the cottage to get this jewel.
- Once you have all 8 jewels, go to Thomas's house. Examine the refrigerator in his home to gain the 9th and final jewel.