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Porcellanite worked into Neolithic axes, Northern Ireland

Porcellanite or porcelanite, is a hard, dense rock somewhat similar in appearance to unglazed porcelain. It is often an impure variety of chert containing clay and calcareous matter.[1]


Porcellanite layer is the black rock above the hammer, and below the brown layer higher up the slope at Tievebulliagh

At Tievebulliagh, Northern Ireland, porcellanite is a tough contact metamorphosed hornfels formed from a lateritic soil horizon within a basaltic intrusive/extrusive sequence. The mineral is black to dark grey in colour. It is the site of a Neolithic axe or stone tool quarry, and there is another quarry on Rathlin Island.[2] It is likely that roughouts or roughly shaped celts were chipped on site before transportation both within Ireland and over the Irish Sea to the British mainland.[citation needed] It is also likey that the final polish would have been performed near the site of use in cutting vegetation and trees.[citation needed] It was commonly polished on grooved blocks of hard sandstone.[citation needed]


  1. ^ The Editors of Encyclopædia Britannica (20 July 1998). "Porcellanite". Encyclopædia Britannica. Encyclopædia Britannica Inc. Retrieved 28 March 2017. 
  2. ^ "Tievebulliagh". Geological Sites in Northern Ireland — Earth Science Conservation Review. Habitas — National Museums Northern Ireland. 3 May 2003. Retrieved 28 March 2017.