"How are minerals made?" "What makes rocks sparkly?" Mary Lou and Tilly are curious about minerals, the chemical compounds that make up rocks! Get ready for a behind-the-scenes tour of the Field Museum in Chicago! Collections manager Jim Holstein opens cabinets containing some of the most exceptional minerals in the world. Find out how scientists have classified minerals for hundreds of years, and why some minerals glow in the dark. Do you have a rock collection? Or any kind of collection? How do you organize, or "classify" it? Check out photos and videos from our tour on the blog at sciencepodcastforkids.comWant to support Tumble, and hear your name on the show? Pledge on our Patreon campaign at patreon.com/tumblepodcast! We LOVE our supporters.