Obsidian is a naturally occurring volcanic glass, distinctive for its smooth texture and sharp edges, formed from lava that rapidly cooled.
Key Characteristics of Obsidian
Obsidian is an extrusive rock that forms when molten rock erupts from a volcano and cools very quickly. Unlike most volcanic rocks, which tend to be rough and jagged due to trapped gas bubbles, obsidian is remarkably smooth. This unique texture is primarily because it consists almost entirely of glass.
Here's a comparison of obsidian's properties to other common volcanic rocks:
| Feature | Obsidian | Most Volcanic Rocks |
|---|---|---|
| Formation | Extrusive, rapidly cooled lava from a volcano | Extrusive, erupted from a volcano |
| Texture | Smooth | Rough and jagged |
| Composition | Mostly glass | Contains gas bubbles (which make them jagged) |
| Breakage Pattern | Breaks like glass, forming smooth, curved shapes with very sharp edges | (Varies, often irregular or granular) |
Due to its high glass content, obsidian exhibits a conchoidal fracture, meaning it breaks with smooth, curved surfaces, much like a broken bottle or piece of window glass. These fractures result in exceptionally sharp edges, historically making obsidian valuable for tools and weapons.
For more information, you can explore resources like the American Museum of Natural History.
