|MadSci Network: Physics|
I don't know the actual rock magnetization numbers. I suspect that the maximum is pretty small. Perhaps up to 4PiMr = 10 G for common rocks. I know that people used small naturally occuring magnetite rocks as a compasses by floating them in water. It is easy to find rocks that can be magnetized. It is much harder to find one that has alrady been magnetized. In order to magnetize a rock one has to have a strong magnetic field. These exist only very rarely in nature. I have heard about rocks being magnetized by being near the point where lightning struck the ground. The field from the very high electrical current is certainly large enough to do the job. I suggest that you go a good technical library and look for a book on Rock Magnetization to get more data. A quick look on Google turned up nothing useful. [note added by MadSci Admin: I found several sites which have some good information and some clues as to the strength of magnetite. See http://scitoys.com/scitoys/scitoys/magnets/magnets.html and http://www.madehow.com/Volume-2/Magnet.html The statement is made in the 2nd reference that NdFeB magnets can be 75 times stronger than magnetite. If one looks at this site http://www.forcefieldmagnets.com/catalog/index.php?cPath=23_37 one finds that their NdFeB magnets have a magnetic strength of about 12000 Gauss, which would imply that magnetite can be as strong as 160 Gauss, but I have no idea if that is typical of natural magnetite. - - John Link, MadSci Physics Admin ]
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