Exterium by Mary Nicholson
Ten-year-old Max is perfect. He has good grades is athletic and honest. The only problem is that he wants to be more like his fifteen year old brother Michael. He is rebellious, couldn’t care less about grades and is always on the lookout for the next adventure.
Max finds his moment when he stumbles upon a precious gem and decides to keep it. Michael discovers this gem and learns it has mysterious powers. Breaking the law together to learn more about it, the boys’ curiosity turns from exciting to deadly when they find themselves on a planet called Exterium. They must pull from each other’s strengths as they struggle to survive. Worse, their time is limited and if they don’t devise a plan soon they will never be able to return to Earth.