Night Crystals: these natural crystals absorb visible light and come in two varieties. Twilight crystals absorb some of the non-magical visible light in the surrounding area, cutting torch and lamp illumination diameters in half. Midnight crystals absorb all non-magical light in their vicinity, making mundane light sources useless.
Chameleon Veins: these naturally occurring swirling patterns of radiation emanate from the rock in underground environments. Their patterns resemble those normally seen by infravision, darkvision, etc. When chameleon veins are present, the patterns of creatures and objects blend in with the background rock so well that infravision, darkvision, etc. are rendered useless.
Silenite: sometimes crafted into brick walls and flagstone floors, this rock absorbs sound. The footfalls of creatures walking across a silenite floor, for example, cannot be heard, and a magic-user inside a silenite-crafted room cannot cast spells.
Amplicite: this stone magnifies sound many times over. The stealthiest footfall on an amplicite flagstone sounds like a mighty hammer blow ringing on an anvil.