"The markings on the side of the stone indicate that it was once set in something."
The Blue Stone of Treason is a treasure item that appears in Resident Evil 4 that can be sold for 3,500₧ by itself. It is a precious gem that can be fitted into the Golden Lynx, along with the Green Stone of Judgement and Red Stone of Faith to increase its commercial value.
It can be found in Chapter 5-3 in the Campsite after Leon fights U3. After killing the Militia Ganados, go down a ladder in one of the tents and there will be a passage to your right. You will see it right away.
- Hamamura, Koichi, ed (2006) (in Japanese). biohazard4 kaitaishinsho revised edition. Famitsu. ISBN 978-4-7577-2638-3.