In this paper we examine the study of minerals from the Renaissance to the early nineteenth century in the light of the work of Michel Foucault on the history of systems of thought. In spite of a certain number of theoretical problems, Foucault's enterprise opens up to the historian of science a vast terrain for exploration. But this is the place neither for a general exegesis nor for a general criticism of his position; our aim here is the more modest (...) one of taking certain points from Foucault's study,The order of things, and seeing how far they can be extended into an area not explicitly considered in that work. (shrink)