Obsidian is a beautiful volcanic glass that forms when molten rock material cools very rapidly, and was a favourite among ancient people worldwide for creating tools. It forms on the earth’s surface along the edges of a volcanic dome or lava flow, such as where lava contacts water or cool air. It is most commonly opaque black but can occur in many variations such as brown, purple and green – as well as some other colours – usually caused by trace elements or other inclusions.
Obsidian is found in many locations across the globe, confined to areas of geologically recent volcanic activity. It is rare to find any obsidian older than a few million years because the glassy rock is destroyed by weathering. Greece is not the only place where significant deposits are found, they are also in Argentina, Canada, Chile, Ecuador, Guatemala, Hungary, Iceland, Indonesia, Italy, Japan, Kenya, Mexico, New Zealand, Peru, Russia, United States and more!
Obsidian breaks with a conchoidal fracture – meaning it breaks into pieces with curved surfaces, producing rock fragments with very sharp edges. From what we know today, the manufacture of obsidian tools by humans dates back to the stone age. Enormous volumes of obsidian flakes at a site reveal the presence of ancient ‘tool factories’. Flakes are the debris left behind when making blades, and cores – such as this one – are the central piece of obsidian used to take the blades from. Producing arrowheads, spear points, knife blades and scrapers, obsidian was so valued by ancient peoples that it was mined, transported and traded over distances of sometimes thousands of miles. One fantastic property of obsidian is that each outcrop source has very specific characteristics, so using an x-ray flourescence machine, archaeological/geological scientists are able to map where obsidian artefacts have been originally sourced from.
Obsidian was used by the Ancient Greek civilizations and the ancient Aztecs as mirrors due to its high reflectivity, and recent studies have found that Pacific Islanders may have used it in tattooing. Obsidian is today still used in modern surgery! It is able to be shaped into blade edges for scalpels that are thinner and sharper than even the best surgical steel – although its use on humans is regulated and varies from country to country. It is also used in jewellery; however it is easy to scratch and chip! All in all, a beautiful and very interesting stone, it is easy to see why it was so important to our ancestors!
REFERENCES AND FURTHER READING
Carter, T and Conreras, DA 2012, ‘The character and use of the Soros Hill Obsidian source, Antiparos (Greece)’, Comptes rendus – Palevol, Vol. 11(8), pp. 595-602.
Kourtessi-Philippakis, G 2009, ‘Lithics in Neolithic Northern Greece: territorial perspectives from an off-obsidian area’, Documenta Prehistorica, Vol 36.
Liritzis, I and Stevenson, CM 2012, Obsidian and Ancient Manufactured Glasses, University of New Mexico Press, Albuquerque.
Renfrew, C 2012, ‘Cyclades’, in EH Cline (ed) The Oxford Handbook of the Bronze Age Aegean, Oxford University Press, New York.
http://geology.com/rocks/obsidian.shtml