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The Magnetization Of Minerals In Rocks

The phenomena observed by Delesse and Brunhes can be explained because of the fact that certain common iron-containing minerals are affected by any magnetic field, including that of Earth. Two of the most important of these minerals are the oxides of iron, magnetite (Fe3O4) and hematite (Fe2O3). When these minerals occur in molten rock, their atoms are free to move in such a way as to align themselves with Earth's magnetic field. When the rocks cool, the minerals are then frozen in position, oriented along the earth's magnetic north-south axis.

Magnetic minerals found in rocks today, however, are not necessarily oriented along Earth's present magnetic north-south axis. They may have shifted slightly in a vertical direction (their inclination or dip) or in a horizontal direction (their declination). The deviation of a mineral's orientation to the present magnetic field is of value in determining changes in Earth's structure in the past.

For example, a magnetic mineral originally laid down along the equator would have an inclination of 0°, while one laid down at one or the other of the poles would have an inclination of 90°. Suppose one finds a rock lying at 40° north latitude with minerals that have an inclination of 0°. Then, one might conclude that this rock originally was laid down along the equator and, by some means, it was transported northward by a distance of 40° of latitude.

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Science EncyclopediaScience & Philosophy: Overdamped to PeatPaleomagnetism - The Magnetization Of Minerals In Rocks, Magnetization Of Minerals, Measurement Of Paleomagnetism, Applications Of Paleomagnetism