This essay examines how the modern concept of the chemical element emerged during the eighteenth century. It traces this concept to a group of assayers, mineralogists, and chemists active at the Swedish Bureau of Mines (Bergskollegium). Driven by a deep ontological pragmatism, these "mining chemists" came to regard all inquiries into the component parts of metals as useless speculation. Instead, metals were treated as immutable species that made mineralogical taxonomy possible. Their work was a form of Enlightenment boundary work, which associated chrysopoeia and the pursuit of the components of metals with superstition and disreputable activities such as astrology.