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Obsidian
Obsidian is a natural volcanic glass: it is a kind of igneous rock. It is produced when lava high in silica (SiO2) cools rapidly, and solidifies quickly.[1] Because there is no crystal structure, obsidian blade edges can reach almost molecular thinness. They were used as arrowheads, and today they may be used as surgical scalpel blades.[2]
- ↑ Obsidian is found in rhyolitic lava flows known as obsidian flows. This lava cools rapidly.
- ↑ Wescott, David (1999). Primitive technology: a book of Earth skills. Gibbs Smith. p. 90. ISBN 978-0-87905-911-8.
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