Crystal of Earth

Patrick describes it as "kind of a magical globe of [the Secret Country], and if you break it, it's like blowing up the country"

he and Ted find what they think is the Crystal of Earth in the North Tower; it is a colorful, "dazzling globe... bigger than Ted's head" and Patrick smashes it with a sword

then when the children go back to the forest after the Unicorn Hunt, Laura tries to change things by saying Patrick didn't break the Crystal of Earth, and then when they go back to the North Tower there is "a globe the diameter of a wading pool" that emits gold light and contains sparkling light of all colors; it is larger than the other globe and, unlike the other, glows