What exactly is lava, and how hot is molten lava? I would have WAGed it was molten iron from deep within the earth, but when you see lava rocks, they are nothing of the kind! Light and flakey, they seem nothing at all like the molten form. (Do they contain any iron?) What gives? - Jinx
Lava is molten rock, not iron, and it varies widely in composition. Cooled lava can range from very light pumice stone, which will float on water, to heavy, dense basalt or glass-like obsidian. Hot lava ranges from 1,300°F to 2,200°F and varies widely in viscosity as well; some flows quickly, like a liquid, other lava moves much mor slowly.
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