Blue-stained Flints

Abstract

Two years ago I found large patches of an intense blue colour, with some black spots, on flints on the quay at Great Yarmouth. I looked for a possible cause, and discovered other patches similar in all respects but colour. The latter patches were black, and had been made by tar spilt by fishermen when tarring their fish skips. I kept some pieces, both black and blue, in a box until some months ago, and no appreciable change had taken place, so I came to the conclusion that the blue colour was produced by the action of the tar on the flint when exposed to sunlight.