Memory crystals are magically enhanced blue quartz, once used to give homunculi and other constructs the ability to remember. Combined with scrying spells, they could preserve information and moving images for later playback.
Their manufacture is an expensive lost art. Toxic exposure could cause lasting damage to the maker’s mind and nervous system, though the precise cause is not fully understood. Surviving crystals are uncommon remnants of a craft whose cost was paid in health as well as wealth.