Rock magnetism

Japanese: 岩石磁気 - がんせきじき（英語表記）rock magnetism

Magnetism remaining in rocks. It is also called fossil magnetism, paleomagnetism, or remanent magnetism. Ferromagnetic minerals such as magnetite were magnetized in the Earth's magnetic field at the time the rocks were formed, and the north of this remanent magnetism is the magnetic north pole at the time the rocks were formed. Remanent magnetism is most prominent in igneous and metamorphic rocks, but it can also be seen in sedimentary rocks where volcanic ash has been quietly deposited. Measurements of rock magnetism can reveal changes in the Earth's magnetic field since the formation of the solid Earth, the reversal of the magnetic north and south poles, and evidence of continental drift.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

岩石の中に残っている磁気。化石磁気，古地磁気，残留磁気ともいう。磁鉄鉱などの強磁性鉱物が岩石生成時の地球磁場の中で磁化したもので，この残留磁気の北が岩石生成時の磁北極である。残留磁気は火成岩，変成岩に顕著であるが，火山灰が静かに沈積した堆積岩にも認められる。岩石磁気の測定から，固体地球ができてからの地球磁場の変動，磁北極と磁南極の逆転，大陸移動の形跡などを知ることができる。

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