The volcanic glass obsidian has a rock solid place as a valuable resource in human history. It also has a solid place in fiction, as the Game of Thrones material of Dragonglass found on Westeros and Essos. In our real world, for thousands of years obsidian has been prized for cutting and piercing tools. It has been used for decorative objects and polished to create early mirrors. Even today it is used for surgical tools. In George R. R. Martin’s universe, Dragonglass is allegedly one of only two substances capable of killing White Walkers (think: ice-zombies). 

Obsidian develops when volcanic lava cools extremely rapidly. Individual atoms “freeze” in place instead of combining with other minerals and forming crystals. Since mineral crystals do not form, obsidian is hard, brittle, and can produce shell-shaped, or conchoidal, fractures when struck. These properties make obsidian optimal for precision chipping, and the glass can produce an extremely thin and sharp edge. Today, well-crafted obsidian blades are still in use, as they have a cutting edge many times sharper than high-quality steel surgical scalpels. Attempts to cast or bend obsidian for tool fabrication, as in the Game of Thrones universe, will not go well, so don’t try this at home. Just because it’s possible by the laws of physics doesn’t mean it’s a good idea. 

In the Andes Mountains above the Pucuncho Basin in southern Peru, alcoves in cliffs of volcanic rock formed ancient shelters. Ceilings covered with soot, walls with rock art, and floor sediments with charred plant and animal remains indicate human occupation of these shelters beginning about 12,000 years ago. Located at the astonishingly high and remote elevations of more than 14,000 feet, what could have motivated ancient people to visit such a cold, treeless, and hostile environment? This should be obvious given the topic of this blog post. Obsidian. The ancient ones collected and worked pieces of obsidian eroding from sediments on the mountain slopes. The artifacts they left behind include an impressive collection of hundreds of obsidian projectile points, scrapers and other tools. 

There are hundreds of active volcanoes in the Andes Mountains, and a handful have produced high-quality obsidian. Glass that is free of crystal inclusions and gas bubbles is imperative for tools. The material must also be of a relatively young age (geologically speaking), as the glass becomes unstable over time and favorable fracturing properties are lost. The rarity of suitable obsidian resulted in the material being traded over long distances in the Andes (described in my forthcoming book). Distinctive geochemical “fingerprints” based on trace element composition allow obsidian from archaeological sites to be matched with the volcanic source, allowing us to see how far these shiny lumps of glass were carried. While it’s amazing that modern science allows us to trace individual shards back to individual volcanoes, to date, no obsidian has been traced back to a dragon. Yet. 


Cover photo: Arenal, Costa Rica –
Obsidian specimen: Image by Hans Braxmeier from Pixabay
Obsidian outcrop: Image by Brian Keast from Pixabay