Definition: The term "geode" means a celestial body, especially the Earth's largest rock formation, a "fairy godmother." It refers to an ancient stone structure formed by sedimentary rocks at the center of the Earth. Definition: A geode is an astronomical object in space that is approximately 7.42 times larger than Earth and has a diameter greater than 80 miles. They are composed of crystals, usually quartz or granite, and are found primarily on moons orbiting planets such as Venus, Mars, and Jupiter. The term "geode" is often used to describe this unique astronomical phenomenon in the solar system.