Magnetic susceptibility measurements in minnesota part ii: analysis of field results

75 samples of 7 rock types have been analyzed for magnetite content by magnetic separation and chemical analysis, making allowance for iron which occurs as ilmenite, hematite, and silicates. Magnetic susceptibility shows a clear dependence on magnetite content but with too much scatter to permit prediction of one from the other. For small magnetite content V (in volume percent), susceptibility k is roughly given by [Formula: see text] cgs. Based on 200 outcrops of 11 rock types, the approximate mean susceptibility of basalt and diabase is [Formula: see text], of rhyolite and gabbro [Formula: see text], of acid intrusives including granite [Formula: see text], of greenstone [Formula: see text], and of slates [Formula: see text]. Variability is high for acid intrusives, intermediate for basalt, rhyolite, and greenstone, and lower for diabase, gabbro, and slate.