Pitchstone

Pitchstone is a dark coloured, glassy volcanic rock formed when felsic lava or magma cools quickly.

Its colour may be mottled, streaked, or uniform brown, red, green, gray, or black.

[1] The pitchstone ridge of An Sgùrr on the Isle of Eigg, Scotland, was possibly formed as a lava flow in a valley.

[2] Pitchstone from the Isle of Arran was used as the raw material for making various items from the Mesolithic through the Neolithic to the Early 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.