Artifacts are very rare objects with mysterious powers. They often confer daily bonus or other advantages. Once collected, artifacts will be kept in your treasure, just like gems.
Artifacts will require gemstones to be powered, but they will not consume them.
All artifacts are completely dormant at the moment and will be able to unfold their powers after the "Gem Powers" mini update.
As opposed to almost every other aspect of our gamification, some artifacts are be limited or even exlusive. Nobody can have them all, not even the admins. The only other known gamification element that can be exclusive are titles.