Lazurite

https://pathfinderwiki.com/wiki/Lazurite

Lazurite is a highly dangerous crystal. In Session 3: http://undahar.wikia.com/wiki/Session_3, players encountered a mine full of ghouls and lazurite crystals and took 75 kilograms home to Taleah. In Session 4, http://undahar.wikia.com/wiki/Session_4, the package they saved from the burning inn contained refined lazurite (and undead babies) and in session 8, http://undahar.wikia.com/wiki/Session_8 , the druids shrine was deviled by lazurite in the ground and it corrupted their ritual. This made the dryad evil and the druids that died undead.