Magnetic susceptibility of bedded iron-formation
Magnetic susceptibility of bedded iron-formation
Geophysics (October 1963) 28 (5): 756-766
The susceptibility of natural and artificial Fe-formation samples in the form of cylinders with length-to-diameter ratio less than 1.2 and susceptibility up to 1 cgs unit was measured in fields of the order of 1 gauss. Demagnetization factors calculated for the centers of the cylinders explain observed changes of apparent susceptibility with length and direction of magnetization. Layered samples made by stacking disks of magnetic and nonmagnetic material alternately show susceptibility as much as 3 times greater parallel to the layers than across them, with layer susceptibility as high as 0.5 cgs. This anisotropy increases with increasing layer susceptibility and is largely independent of the details of layering when less than half the volume of the sample is magnetic material. Natural layered samples show the same range of susceptibility anisotropy. The relationship between susceptibility, k, and volume % magnetite, V, can be approximated by k=0.00116 V (super l.39) cgs, 10<V<40, corresponding to susceptibility 0.7 for pure magnetite The along-the-layer susceptibility of a bedded sample containing 20 volume % total magnetite is twice that a homogeneous sample of the same over-all magnetite content. For 1% total magnetite, it is 3 times as great.