Elizabeth Emma Ferry traces the movement of minerals as they circulate from Mexican mines to markets, museums, and private collections on both sides of the US-Mexico border. She describes how and why these byproducts of ore mining come to be valued by people in various walks of life as scientific specimens, religious offerings, works of art, and luxury collectibles. The story of mineral exploration and trade defines a variegated transnational space, shedding new light on the complex relationship between these two countries and on the process of making value itself.