Pitchstone is a dark coloured, glassyvolcanic rock formed whenfelsiclava ormagma cools quickly. Since it is avolcanic glass, pitchstone may have aconchoidal fracture. Pitchstones may also containphenocrysts, in which case it is a form ofvitrophyre. Pitchstone has aresinouslustre, or silky in some cases, and a variable composition. Its colour may be mottled, streaked, or uniform brown, red, green, gray, or black. It is anextrusive rock that is very resistant toerosion.[1]
The pitchstoneridge ofAn Sgùrr on the Isle ofEigg,Scotland, was possibly formed as a lava flow in a valley.[2]
Pitchstone from theIsle of Arran was used as the raw material for making various items from theMesolithic through theNeolithic to theEarly Bronze Age.[3] Mesolithic use appears to have been limited to the Isle of Arran itself, while in later periods the material or items made from it were transported around Britain.[3]
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