[1] Gems and Gemstones: Timeless Natural Beauty of the Mineral World, By Lance Grande
[2]Archived 2022-11-01 at the Wayback Machine Gems and Gemstones: Timeless Natural Beauty of the Mineral World, By Lance Grande
Slavchev, Vladimir (2010). "The Varna Eneolithic Cemetery in the Context of the Late Copper Age in the East Balkans". In Anthony, David; Chi, Jennifer (eds.). The Lost World of Old Europe: The Danube Valley, 5000-3500 BC. New York University, Institute for the Study of the Ancient World. pp. 192–211. ISBN9780691143880.
"The Varna Treasures; Archaeological Museum, Varna". Thracian Treasures from Bulgaria: Checklist of The Special Exhibition, June 11 – September 4, 1977, coordinated by Dietrich von Bothmer, items 20–74. New York: Metropolitan Museum of Art. 1977. Archived from the original on 6 July 2018. Retrieved 6 July 2018 – via Digital Collections of the Metropolitan Museum of Art.
"The Varna Treasures; Archaeological Museum, Varna". Thracian Treasures from Bulgaria: Checklist of The Special Exhibition, June 11 – September 4, 1977, coordinated by Dietrich von Bothmer, items 20–74. New York: Metropolitan Museum of Art. 1977. Archived from the original on 6 July 2018. Retrieved 6 July 2018 – via Digital Collections of the Metropolitan Museum of Art.