If you find a piece of obsidian in the field, you have discovered an intrusive, plutonic igneous rock meaning it crystallized inside the Earth over a long period of geologic time.

Name: If you find a piece of obsidian in the field, you have discovered an intrusive, plutonic igneous rock meaning it crystallized inside the Earth over a long period of geologic time.
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Obsidian is an extrusive, volcanic igneous rock that is formed from quickly cooling lava at the Earth's surface.

If You Find a Piece of Obsidian in the Field