1. ^{{cite journal|url=http://connection.ebscohost.com/c/articles/90546894/polished-stone-tools-from-late-neolithic-site-hadzhidimitrovo-yambol-district-rocks-specifics-raw-material-procurement |title=Polished stone tools from the Late Neolithic site Hadzhidimitrovo, Yambol district: rocks and specifics in raw material procurement. |last=Hadzhipetkov |first=Iliya |journal=Proceedings of the Bulgarian Geological Society|year=2011 |volume=72 |issue=1-3| page=53|quote=The analysis of polished stone tools from the Late Neolithic site Hadzhidimitrovo shows a direct link between the raw material and technology used in its treatment. It is associated primarily with knowledge of how to facilitate the work process and how to increase stability of tools at work.}}