The Rev. Dr John Walker was the Professor of Natural History at the University of Edinburgh from 1779 to 1803. Although his time in this position has been addressed by several studies, the previous thirty years that he spent ‘mineralizing’ have been virtually ignored. The situation is similar for many of the well-known mineralogists of the eighteenth century and there is a lack of studies that address how a mineralogist actually became a mineralogist. Using Walker's early career as a guide, this essay seeks to detail the making of an eighteenth-century Scottish mineralogist. The time frame under examination begins with Walker's matriculation at the University of Edinburgh in 1746 and it ends with his being appointed professor in 1779. The first section demonstrates that Walker's early mineralogical education at the Medical School and under William Cullen was closely linked to chemistry. The second section shows how he used chemical characters to classify minerals and to criticize the systems of Linnaeus, Da Costa, Wallerius and Cronstedt. Because Walker needed many ‘fossil’ samples to test the viability of his chemical mineralogy, the final section details how he used tours, patrons and correspondents to build his mineral collection.