The Apollo missions are most celebrated for putting human footprints on the moon, but their biggest contribution to science was the collection of rocks the astronauts brought home with them. To call these 382 kilograms of stone and regolith (the thick layer of crushed rock and dust that covers the surface of the moon and other planetary bodies) a treasure trove does not do them justice. Studying these samples in laboratories on Earth helped to establish the modern field of planetary science and gave us crucial insights into geologic processes that operate on all planetary bodies.