The distribution and sources of archaeological pitchstone in Britain

Pitchstone is a glassy volcanic rock, distinguishable from obsidian by having a higher water content. It forms lava flows and minor intrusions at several centres within the British Tertiary Volcanic Province (BTVP) in the west of Scotland and Ireland. Pitchstone artifacts and waste pieces have been recorded from 101 archaeological localities in Scotland and northern England, ranging in time from possibly Mesolithic to Bronze Age. To characterize the sources, 17 pitchstone samples from 11 sources within the BTVP were analysed for major elements by energy-dispersive X-ray fluorescence (EDXRF), and for trace elements by instrumental neutron activation analysis (INAA). 28 pitchstone pieces from 22 archaeological sites were analysed, mainly non-destructively, by INAA and interpreted as having originated from Arran sources. The Arran sources are divided into four petrographic types; the Corrygills, Tormore, Glen Shurig and Glen Cloy Types. Petrographic study of 15 archaeological samples indicated that three were of Corrygills type and two were of Tormore type. The remainder were less confidently attributed to the petrographic types distinguished. Arran pitchstone is found as far as 300 km from the Arran sources, at the chambered tomb of Ord North in Highland.