Barite, or Baryte, BaSO4 is barium sulphide. This specimen is peculiar to cliffs on the north coast of the Isle of Sheppey, in Kent. The cliffs, which are in the London clay, are host to large septarian nodules. The nodules have cracks which are lined with pale mustard coloured calcite, on which there are radiating greyish white barite crystals. How this type of mineralisation occurs seems to be a mystery.