Which igneous rock is typically glassy and forms when lava erupts rapidly?

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Multiple Choice

Which igneous rock is typically glassy and forms when lava erupts rapidly?

Explanation:
Rapid cooling of lava at the surface prevents crystals from forming, creating a glassy texture. That glassy volcanic rock is obsidian, which forms when lava erupts quickly and quenches into a smooth, glassy solid that often fractures conchoidally. The other rocks—granite, diorite, and gabbro—cool more slowly and develop visible mineral grains, developing crystalline textures instead of glass.

Rapid cooling of lava at the surface prevents crystals from forming, creating a glassy texture. That glassy volcanic rock is obsidian, which forms when lava erupts quickly and quenches into a smooth, glassy solid that often fractures conchoidally. The other rocks—granite, diorite, and gabbro—cool more slowly and develop visible mineral grains, developing crystalline textures instead of glass.

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