Obsidian

Obsidian is natural volcanic glass formed when silica-rich lava cools too quickly to crystallize. Its conchoidal fracture produces exceptionally sharp edges, making it useful for tools and valued objects.

Felsic lava: Silica-rich molten rock that is typically viscous and erupts at relatively low temperatures. Obsidian commonly forms when silica-rich lava cools before crystals can grow.
Obsidian knapping: The shaping of obsidian by striking or pressing flakes from a larger piece. Knapping turns obsidian’s predictable fracture into blades, points, and cutting tools.
Obsidian hydration: The gradual diffusion of water into a freshly exposed obsidian surface. Hydration begins when knapping exposes a new surface, leaving a time-dependent layer.
Ubaid obsidian trade: The movement of obsidian into communities of the Ubaid period in ancient Mesopotamia. Ubaid-period artifacts document early exchange of obsidian beyond its volcanic sources.
Flint: A hard sedimentary rock composed mainly of microcrystalline quartz, widely used for prehistoric tools. Flint also flakes into sharp edges, but it is crystalline rock rather than volcanic glass.
Volcanic glass: Natural glass formed when molten rock cools too rapidly for crystals to develop. Obsidian is the best-known natural example of this noncrystalline material.
Obsidian projectile point: A pointed weapon tip made from obsidian and attached to a spear, dart, or arrow. Projectile points show how its sharp flakes served hunting and warfare.
Obsidian sourcing: The identification of an obsidian artifact’s geological source through its chemical or physical signature. Source matching maps the movement of obsidian from volcanic deposits to archaeological sites.
Clovis points: Distinctive fluted stone projectile points associated with the Clovis archaeological culture of the Americas. Some Clovis points were made from obsidian, linking the material to early American toolmaking.
Chert: A fine-grained sedimentary rock made chiefly of microcrystalline silica. Chert can resemble obsidian as a toolstone, but lacks its glassy volcanic structure.

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