This is exactly what it sounds like. It’s a sphere, made of glass or quartz crystal used by clairvoyants for scrying and divination. The crystal balls come in various different sizes, from small spheres that can be worn as jewelry to large domes that sit on tabletops. There’s no magic in the sphere itself. It is used as a tool for focus, so the clairvoyant can see images in order to get messages from the spirit realm and the elemental kingdoms.