The illustrations show spherulitic siderite (FeCO3). This specimen is from a loose block found on the shore near Long Nab, Burniston, North Yorkshire, no doubt from one of the bands of carbonaceous clay. The mineral is associated with plant material and palaeosols ("fossil soils"). Each spherule averages 1-1.5mm in diameter.  A. Thin section in plane polarised light. B. Same thin section in crossed polars. C. A thin section in crossed polars, but using a scanner.

The bottom right picture is a scanned photo of a polished section. The pictures show sphaerosiderite set within a matrix of carbonaceous silty clay material. Notice the typically low birefringence of the quartz grains in B. The spherule in A and B is 1.5mm wide. B and C illustrate a radial structure in the cores of the spherules. C and the bottom right photo's show each spherule rimmed with a brown mineral, probably an iron oxide due to reaction with the clay minerals.

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