These large convex GO stones are made of high quality ABS plastic. Crafted to perfection. Every stone is high quality and made to last. They go great with a larger Goban. Go emphasizes balance and constructive focus and teaches restraint and cooperation, and it engages more areas of the brain and may even produce physical changes. Go players utilize higher-order thinking skills, analyze actions and consequences, and visualize future possibilities. Each time the game is played, these skills are strengthened.