You found an ancient tome about gems.
You should bring it to the jeweler in the Gates of Morning.
This quest is triggered when you find the Ancient Tome titled 'Gems and their uses', a special artifact found only in the Far East. As directed, take it to Limmir in Gates of Morning; he can be found south of the main road roughly halfway across the city.
Limmir will explain that the tome gives details on creating really powerful magic amulets, but that you need to find the Valley of the Moon in the southern mountains and summon Limmir there via a scroll he provides. Note that talking to Limmir about the book will permanently remove him from Gates of Morning, and his crafting services can not be accessed until you complete the quest.
The final level of the Valley of the Moon contains an island full of huge glimmerstones; use the scroll here to summon Limmir. Limmir will enter the map from the northeast and walk to a place directly southwest of the glimmerstones. Once there, he will start a ritual to purify the area, and a count-down turn timer will appear. Also, various demons will begin spawning from the three portals in the northeast. Your task is to keep Limmir alive until the timer reaches zero. If you manage that, then all demons are removed from the area, and Limmir will offer you a special service: For a small fee, he will imbue amulets with two gems per amulet, as long as the gems are different. These amulets are called Limmir's Amulet of the Moon, regardless of what they are made of.
After the quest, Limmir will remain in the Valley of the Moon, where you can visit him if you desire his services. Limmir will craft as many two-gem amulets as you like (provided you have the necessary resources and gold), and he will also craft rings again (though just with a single gem).