Stone of Schueler

The Stone of Schueler was an artifact of the Church of God Awaiting, a blue crystal that could tell if a person spoke the truth.

According to legend, it was entrusted to the Wylsynn Family by the Archangel Schueler himself. Many centuries later Paityr Wylsynn kept it hidden in his Scepter of Langhorne while serving as Intendant in Charis. Upon receiving orders from Erayk Dynnys to investigate the leadership of Charis, he revealed the existence of the Stone to King Haarahld VII, Crown Prince Cayleb, and Merlin Athrawes. He tested each of them with the device, finding them all to be truthful.

It was actually a disguised verifier, an advanced lie detector developed by the Terran Federation. 

When mated to the Key of Schueler the Stone can produce a hologram of the Archangel Schueler, which mentions a powerful weapon that can only be used once, in the time of greatest need of the Church.

The Stone’s existence was known to most people of Safehold, although most people believe it was lost forever around the time of Saint Evrahard's death.