Natural Science in Archaeology

4.4 Obsidian 85
4.4 Obsidian
Obsidian is a natural volcanic glass that is found in rich deposits around some young
volcanoes. It has been used for making flaked tools since the Paleolithic. Obsidian
helped several ancient civilizations develop before the onset of metal tools. Among
Neolithic societies obsidian was traded widely because it had more workability and a
sharper edge compared with competing materials. Obsidian was extensively available
in some regions, entirely absent in others. Obsidian was such a near-perfect lithic material
that it was traded over great distances. In the early Holocene a site on the northern
Tibetan Plateau utilized obsidian from a source 416 km away (Brantingham and Xing
2006). This is especially surprising considering the difficulty of travel in that terrain.
The name obsidian goes back as far as Pliny who described material from
Ethiopia. Recent provenance studies have shown that artifact obsidian from the
Middle Stone Age of Ethiopia came from as far away as 250 km. (Negash and
Shackley 2006) High-silica volcanic rocks are typically very fine-grained or glassy.
The molten material from which these rocks formed is so extremely viscous that
crystal growth is impeded and noncrystalline rocks often form during rapid cooling.
With its conchoidal fracture, obsidian is easily worked into very sharp projectile
points and other implements, so has had wide usage since prehistoric times.
Obsidian is usually black but may be gray, brown, red, or green. The fracture surface
of obsidian is perfectly conchoidal. Generally, obsidian is rhyolitic in composition
and contains less than 1% H 2 O. The atomic arrangement of obsidian is that of a glass.
Compositionally, obsidian is high in silica. Volcanic glasses form with difficulty in
mafic magmas, such as those with basaltic composition, which have less silica. Only
the rare palagonite, sideromelane, tachylite, and hyalomelan are obsidians with basaltic
composition. Lassenite is related to obsidian but with a trachytic composition.
In the East African Rift Valley volcanic belt, obsidian was exploited throughout
the Paleolithic (Ambrose 1998). At many sites it was the preferred material (Leakey
1931; Robertshaw 1988). Obsidian was utilized at least as far back as Upper Paleolithic
times in the Near East. It was found in level C of the Shanidar Cave in Iraq and
dated to approximately 30,000 BP. Obsidian has been recovered from almost every
Neolithic site in the eastern Mediterranean area.
Approximately 1000 western Mediterranean sites contain obsidian, dating from
the early Neolithic (6000 BCE) (Pollmann 1993). The important Lipari obsidians
are discussed by Cortese et al. (1986). Figure 4.10 shows the major obsidian deposits
of Europe. Neolithic sites in Anatolia are particularly rich in obsidian artifacts.
In Anatolia, rich obsidian deposits were formed from volcanism in the Tertiary and
the Quaternary. These deposits are present around young volcanoes such as Suphan
Mountain, Nemrut Mountain, Tendurek Mountain, and Agri Mountain in East Anatolia,
and Hasan Dag Mountain and Erciyas Mountain in Central Anatolia. Obsidian
deposits also occur near Rize, Erzincan, Erzurum, around Bingöl, and between Bolu
and Ankara. Obsidian deposits also exist in Erivan (Yerevan), Armenia, and on the
island of Melos, Greece. Eastern Mediterranean obsidian was used not only for making
tools, but also for mirrors and decorative goods. Figures 4.10 and 4.11 show the