A section through the Upper Cambrian alum shales at Hynneberg, Närke, central Sweden, has been investigated chemically and mineralogically. The mineral constituents were examined qualitatively by X-ray and their quantitative distribution was calculated from chemical analyses. The main minerals found were micaceous minerals, pyrite and quartz. The organic fraction was enriched by a flotation process and its composition was found to be almost constant at C10H11O throughout the section. Small amounts of S and N were also found in the organic matter.