<p>The article examines the <i>Mineralogica</i> chapter of the <i>Ephemeris</i> by the Ulm city physician Johannes Franc (1645–1725), in which mineralogical observations, early modern natural philosophy and Franc’s practical experience with urinary stones intersect. In his daily practice, Franc treated numerous patients suffering from urolithiasis, employing plant-, animal- and mineral-based remedies, while surgical interventions remained the responsibility of specialised lithotomists. His interest in mineral structures was sparked by the discovery of a naturally occurring stone shaped like an orchid, which reminded him of a finger-shaped urinary stone painfully expelled by his patient Litzelhirn in 1679. This analogy prompted Franc to interpret natural and pathological stone formations in parallel. In his theoretical reflections he draws on Paracelsian models, which assign kidneys and bladder to the influence of Venus (copper), as well as on G.B. de Saint-Romain’s descriptions of crystalline structures in antimony regulus. On this basis, he seeks to integrate the formation of secondary concretions of the excretory organs – including kidney stones, bladder stones and other gastroliths – into a cosmological and metallurgical framework. A particular focus lies on bezoars and uroliths. Using excerpts from Robert Boyle’s <i>Exercitationes</i>, Franc discusses the actual medical efficacy of these concretions. Boyle reports on stones removed from human bladders, to which – despite their low esteem – a pronounced diuretic and sudorific effect was attributed (<i>urinam et sudores ciere</i>). Franc employs these observations to reflect both on the possible therapeutic relevance of bladder stones and on their supposedly “planetarily” influenced structure and formation.</p>