Obsidian: A Glassy Rock For Toolmaking

Volcanoes erupt and some of them extrude felsic lava. This lava of high temperature meets air or, sometimes, water and it may cool rapidly. It is how obsidian, a kind of volcanic rock, is formed. Obsidian, also called volcanic glass, is mainly composed of silica in addition to other various contents. Chemically, it has a similar composition to rhyolite and granite. Yet, unlike those, obsidian lacks a crystal structure as the rapid cooling that the lava undergoes after extruding prevents crystal formation.

Obsidian is mostly seen in its black form although there are reddish, greenish, and brownish varieties resulting from its contents such as iron oxide and magnetite. In addition to those, colorless and patterned forms exist as well. Regardless of its color, this glass has a very shiny surface that makes it difficult to go unnoticed. Furthermore, due to its hardness and brittleness, breaking the obsidian results in creating sharp and smooth edges.

As humans, we fell in love with this raw material from the very early ages which goes back as old as Lower Paleolithic (ca. 2.6 million to ca. 200.000 years ago). It was because obsidian is perfect for making sharp tools such as blades, arrowheads, and scalpels. In addition, it was used to make mirrors and decorative objects. As the exploitation, manufacture, and trade of obsidian existed in many parts of the world from very early on, it plays an important role in understanding the human past.  Through certain analyses, the obsidian finds can reveal where their raw material was exploited and when they were produced. How and when our ancestors dealt with obsidian as well as in which directions its commerce took place among various communities are some of the questions that archaeologists ask when they encounter this material on ancient sites. Today, obsidian is still used in making surgical tools as it is superior to steel regarding its evenness. However, the fragile nature of obsidian reduces its use in surgeries to a limited area. 

Photo: An assemblage of Early Cycladic obsidian blades from Milos, Greece (retrieved from Zde, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons)

Bibliography:

“Obsidian.” Encyclopedia.com, Encyclopedia.com, 22 Aug. 2022, https://www.encyclopedia.com/earth-and-environment/minerals-mining-and-metallurgy/mineralogy-and-crystallography/obsidian.

“Obsidian.” Wikipedia, Wikimedia Foundation, 12 Aug. 2022, https://en.wikipedia.org/wiki/Obsidian.

“Obsidian Rock (Mineraloid) Properties, Uses, Formation...” Geology Science, 24 Jan. 2022, https://geologyscience.com/minerals/obsidian/.