Igneous rock
An igneous rock forms when molten rock cools and solidifies, such as basalt or the eucrite meteorites.
An igneous rock is one that formed from molten rock, called magma underground and lava at the surface. When it cools, crystals grow and lock together. Granite and basalt are familiar igneous rocks on Earth.
Many achondrites are igneous. Eucrites are basalts that erupted or intruded on the asteroid Vesta. Shergottites and nakhlites are igneous rocks from Mars, and many lunar meteorites are basalts from the Moon's dark plains. Angrites are some of the oldest igneous rocks known, crystallising within a few million years of the Solar System's birth. Iron meteorites also formed by igneous processes, as molten metal crystallised in asteroid cores.
The texture of an igneous rock reveals its cooling history. Coarse crystals suggest slow cooling deep underground; fine crystals or glass suggest rapid cooling at the surface. Chondrules, though they formed from melt droplets, are not usually called igneous rocks because they cooled in space as free-floating drops.
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Level: Explorer Ages 10 and up