A dark, fine-grained volcanic rock that forms when lava cools quickly at the Earth’s surface. It often appears in large flows or in tall, column-like shapes.
It comes from Latin “basaltes,” used by ancient writers for a hard black stone, which may itself come from a misreading of a Greek word. The exact original meaning is uncertain.
Basalt makes up much of the ocean floor and many giant lava plains, so you’re literally walking on it more than you realize. Those striking hexagonal rock columns you see in photos are often basalt naturally cracking into geometric shapes.
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