obsidian as black gold-- 8/19/26

19 Aug 2026

obsidian as black gold-- 8/19/26

0 COMMENTS

Today's encore selection -- from Mountains of Fire by Clive Oppenheimer. Obsidian was a prized object in ancient times—and it's still prized today for the value of the information it provides to archeologists:

“Some archeologists refer to obsidian as ‘black gold’ owing to its prestige in prehistoric times. It is among the resources that volcanoes offer up.

“While archaic humans already exploited obsidian a million years ago, it was our own species that learned to fashion it with flair in Africa in the Middle and Later Stone Age over the last quarter of a million years. The very word ‘obsidian’ has an African connection, as we learn from Pliny’s Natural History: it derives from Obsidius, a Roman consul who is said to have discovered the rock in Ethiopia. Figuring out how to turn brittle obsidian into precision implements may even have helped to drive wider social, cultural and behavioural change.

“I wonder if our Stone Age ancestors loved it for its lustre and gleam as much as its keen edge.

“Obsidian is extremely useful, too, for modern day archaeologists, who use it to reveal the human geography of the unwritten past. A magma reservoir in the Earth’s crust evolves chemically and physically over time. It cools and slowly crystallises. Denser minerals settle out, depleting the remaining molten rock in magnesium and iron, while enriching it in silicon. The magma can also melt the rock at its walls, and sometimes two different magmas connect and mingle. These myriad processes impart a particular bouquet to the molten rock – like wine, magma is defined by its terroir. The equivalent of a sommelier for magma is an igneous geochemist.

“A skilled one could immediately discriminate between a bull-bodied Californian andesite and a gritty Auvergne mugearite.

Polished snowflake obsidian, formed through the inclusion of cristobalite crystals

“However, most volcanic rocks contain assemblages of common minerals, such as olivine, quartz and feldspar. If handed a piece of lava and its bulk chemical composition, our connoisseur would struggle to identify the individual volcano that gave birth to it. Crystal-free obsidian, on the other hand, has a unique geochemical fingerprint defined by the amounts of different elements. If two obsidian tools have the same print, they were made with the same source rock; if a tool’s print matches that of an outcrop, that is where the raw material came from.

“The technique was pioneered in the 1960s for the Mediterranean, where rich obsidian sources are found on Sardinia, Lipari and Melos. For an archaeologist finding obsidian tools in Tunisia, for example, it is as if they are stamped ‘Made in Italy.’ Obsidian sources are found in most of the volcanic belts of the world – including the Americas, Oceania, the near East, and Northeast and Southeast Asia – so the method is widely applicable. It provides direct evidence for the ranges over which people could exchange ideas as well as pieces of stone, yielding unique insights into prehistoric human culture, mobility and cooperation, even in the absence of a single human fossil. For a volcanologist, it offers a perfect point of collaboration with archaeologists.”