To obtain a Damaged Prism, you need to find and destroy Primal Constructs. The higher the level of the Primal Constructs you destroy, the more of these items they will drop.
You can also trade in Stardust for Damaged Prisms. They cost five Stardust a piece on the Stardust exchange. We don't really recommend doing this, though, as they can be obtained easily via gameplay.
Primal Constructs can be found in the Hypostyle Desert in Sumeru, primarily in the underground ruins. You can refer to the map below for locations:
- Type: Common Ascension Material
Three Damaged Prisms + 50 Mora = One Turbid Prism