Definition of pitchstone in English:

pitchstone

noun

Geology
  • [mass noun] A dull vitreous rock resembling hardened pitch, formed by weathering of obsidian.

    • ‘Similarly, Arran pitchstone has turned up in Ireland and Orkney, highlighting the complex exchange networks between these places.’
    • ‘Also found was a flake of green Arran pitchstone, thought to be a waste fragment from the manufacture of a tool.’
    • ‘This feature was once described as ‘the finest ‘small’ mountain feature in the British Isles ’, and is in reality an east-west ridge of volcanic rock which appears as a narrow upthrust of columnar pitchstone when seen from the south or east.’

Pronunciation:

pitchstone

/ˈpɪtʃstəʊn/