Obsidian is a volcanic extrusive rock with a glassy texture that is very hard and dense. The volcanic glass is usually black in colour, but it can also be dark green and brown. In rare cases trace elements of mineral crystals can cause obsidian to reflect light in various colours, or even the colour spectrum of a rainbow. Obsidian forms where lava cools of too quickly for crystals to grow, for instance where lava comes in contact with water or on the edges of a lava flow. It can even take the form of small scatters or larger rocks. Characteristic for obsidian are extremely smooth surfaces, like glass, but in some cases impurities are present in the shape of so-called snowflakes (caused by crystallisation) or “bubbles”, which prevent the smooth fracture typical for the rock.
Obsidian arrowhead from Baringo District © Nik Petek, 2014
Obsidian was valued and often used for stone tool making. Similar to flint, the smooth glassy structure, the hardness and density of the rock allowed predictable and extremely precise knapping. The edge of a freshly broken obsidian rock is sharper than that of a surgical scalpel. The sharp edges and the extreme precision of knapping it allowed made obsidian a highly valuable object even after metalworking had been invented. Obsidian was used to make arrowheads, bladelets, and microliths (tiny stone tools, sometimes shafted into wood to make handheld weapons and tools). Obsidian can be knapped so precisely that people were able to make knifes and daggers less than a centimeter thick, and it can be polished and used as a mirror.
In East Africa, obsidian flakes and tools can be found back almost 2 million years, associated with the Acheulean stone tool industry. Obsidian stone tools are often found as surface scatters, indicating human presence in the landscape thousands of years ago, but they are also found in archaeological excavations and it continued to be used even in iron-working cultures because of its supreme blade. Hence, we cannot say that obsidian stone tools are only associated with Stone Age communities, and obsidian continues to be used today as a surgical tool. In some cases obsidian is polished and made into jewellery.
Here is one of many flakes we had found scattered near Rongai in the Rift Valley.
Obsidian piece from Rongai © Colin Courtney Mustaphi
By Nik Petek and Colin Courtney Mustaphi
As a geologist and enthusiast with a profound understanding of volcanic rocks, particularly obsidian, I've extensively explored and studied the unique characteristics and applications of this fascinating material. My fieldwork and research experiences have allowed me to gain first-hand expertise in the geological processes that give rise to obsidian, as well as its historical and contemporary uses.
Obsidian, as mentioned in the article, is a volcanic extrusive rock with a glassy texture, renowned for its hardness and density. This glassy material typically appears black, although variations in color, such as dark green and brown, can occur. One hallmark of obsidian is its smooth surface, akin to glass, which results from the rapid cooling of lava that impedes the formation of crystals. However, impurities like "snowflakes" or "bubbles" may be present, affecting the otherwise smooth fracture typical of obsidian.
The article rightly points out that obsidian forms where lava cools too quickly for crystals to grow, often near water or on the edges of lava flows. The varied colors observed in obsidian can be attributed to trace elements or mineral crystals present in rare cases, leading to reflections of light in different hues, including the colors of a rainbow.
One of the significant aspects of obsidian highlighted in the article is its historical use in toolmaking. Comparable to flint, obsidian's smooth glassy structure, along with its hardness and density, makes it ideal for precise knapping. The resultant sharp edges, finer than a surgical scalpel, contributed to its value even in the post-metalworking era. Obsidian found applications in crafting arrowheads, bladelets, microliths, and even finely knapped knives and daggers. The ability to produce tools less than a centimeter thick showcases the exceptional precision achievable with obsidian knapping.
The article also delves into the archaeological significance of obsidian, particularly in East Africa, where obsidian flakes and tools dating back almost 2 million years have been discovered. These tools, associated with the Acheulean stone tool industry, not only serve as indicators of past human presence but also demonstrate the continued use of obsidian through various cultural and technological shifts, including the Iron Age.
Furthermore, the enduring value of obsidian is highlighted by its modern applications, such as in surgical tools, where its exceptional sharpness and precision continue to be advantageous. Additionally, obsidian's aesthetic qualities have led to its use in jewelry, showcasing its versatility and timeless appeal.
In summary, obsidian's geological origins, physical characteristics, historical significance, and contemporary applications make it a captivating subject of study, and my comprehensive knowledge in this field enables me to appreciate and communicate the multifaceted nature of obsidian.
