English: "Typical textural and compositional features of the Soom Shale sediment. (a)–(g) are petrographic images and (b) and (c) are scanning electron microscope backscattered electron images. (a) Typical intercalated homogeneous facies (four lighter layers) and dark, organic-rich laminated facies. The white patches represent clusters of quartz grains (see also (c), (d), (e) and (g)), which almost exclusively occur within the dark, organic-rich layers of the laminated facies. (b) Intercalated homogeneous and laminated facies. Here, pyrite framboids and microcrystals (bright grains) are confined to the laminated facies, probably precipitating within the organic-rich layers. In the centre of the image a cluster of large quartz grains (dark grey) occurs, bounded below by a pyrite-rich layer. (c) A cluster of grains in the laminated facies, comprising dominantly quartz (dark grey) with a few large clay grains (elongate, light grey grains); pyrite (bright grains) occurs around the cluster and denotes the likely position of organic matter (algae?). (d) An elongate cluster of quartz grains in the laminated facies. (e) Small, tightly packed quartz cluster. (f) A large and isolated quartz grain within a thin organic-rich layer. (g) Homogeneous facies (bottom) and laminated facies (top); within the latter lighter, brown lenses and layers occur; these are composed of mud"