Mann, L. M., Scott, A. and Petrie, W. M. F. (1918) “The Prehistoric and Early Use of Pitchstone and Obsidian: With Report on Petrology; and a Note of Egyptian and Aegean Discoveries”, Proceedings of the Society of Antiquaries of Scotland, 52, pp. 140–149. doi: 10.9750/PSAS.052.140.149.