Why are some rocks magnetic?
Quick Answer
Some rocks contain magnetic minerals, especially magnetite, which can preserve Earth’s magnetic signal. These minerals respond strongly to magnetic fields.
The Full Story
Magnetite is one of the main minerals that makes a rock magnetic because its iron-rich crystal structure can align with a magnetic field. In igneous rocks, magnetic minerals can lock in the direction of Earth’s field as lava cools, creating a record of ancient magnetism. This is important for paleomagnetism and helped scientists understand seafloor spreading. Basalt from the ocean floor is especially useful because its magnetization forms alternating magnetic stripes on either side of mid-ocean ridges.
Key Facts
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"A rock can act like a time capsule for Earth’s magnetic field."
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