"Mark Godden's Little Bit Of Cyberspace Mk.II"

Portland Blue

The thick slatt or "Portland Blue" is the only part of the Lulworth formation on Portland that has any potential use as a masonry stone. Similar in both age and appearance to many of the low bedded limestones quarried in the Purbeck district, it can be cut, polished and typically manufactured into flooring tiles and worktops etc. Portland blue has been occasionally carved but its hardness makes this difficult for all but the most experienced craftsman. The infilled crack visible in the lower half of the picture is a typical feature, it clearly illustrates how ground water moving through the crack over millennia has leached the blue / grey iron sulphide stain, present throughout most of the specimen, from cracks' margins.