MAGNETIC SUSCEPTIBILITY OF BEDDED IRON‐FORMATION

Abstract

The susceptiblity of natural and artificial iron‐formation samples in the form of cylinders with length‐to‐diameter ratio less than 1.2 and susceptibility up to one cgs unit was measured in fields of the order of one 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 three 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 percent magnetite, V, can be approximated by [Formula: see text] cgs, 10<V<40, corresponding to susceptibility 0.7 for pure magnetite. The along‐the‐layer susceptibility of a bedded sample containing 20 volume percent total magnetite is twice that of a homogeneous sample of the same overall magnetite content. For one percent total magnetite, it is three times as great.