Soils formed on basaltic substrates commonly have large concentrations of iron oxide minerals, the magnetic behavior of which sometimes seriously hampers the performance of electromagnetic sensors for the detection of buried land mines and unexploded ordnance (UXO). The magnetic properties of soils result from the presence of iron oxides in different forms and quantities, both pedogenic and lithogenic. Paramagnetic and antiferromagnetic iron oxides such as goethite and hematite are abundant in soils but play a minor role in determining the magnetic character of soil. Ferrimagnetic minerals such as magnetite and maghaemite are the most magnetic of the iron oxides, and are of primary importance in their effects on geophysical sensors. Previous work has shown that two magnetic effects in soils pose a large problem for magnetic and electromagnetic sensors: induced magnetization (IM) and viscous remanent magnetism (VRM), both of which can be estimated by measuring the magnetic susceptibility of the soil. The causes of the variability in IM and VRM are not well understood. We present the results of laboratory studies of magnetic properties and mineralogy of 6 soils on the Big Island of Hawaii, with substrate ages of approximately 0.375 to 0.43 My, and 1 soil on O'ahu, with a substrate age of approximately 3.7 My. The mean annual rainfall for the sampled soils on the Island of Hawaii ranges from 180 to almost 5500mm/yr. We have studied the magnetic susceptibility (IM) and frequency dependent behavior of the magnetic susceptibility (a measure for VRM) using a Bartington MS2 magnetic susceptibility sensor in the field (D-loop) and the laboratory (dual frequency B-sensor). Measurements of the magnetic susceptibility at two frequencies allow for the estimation of the presence of ultrafine ferrimagnetic minerals, usually associated with soil formation. The soil mineralogy has been studied with X-Ray Diffraction (XRD), X-Ray Fluorescence Spectroscopy (XRF), differential thermal analysis (DTA/TGA), and chemical extractions. The development of the soils on the Big Island of Hawaii, despite being of similar age, varies strongly with altitude and position on the island. The data indicate a strong negative correlation between mean annual precipitation and induced magnetization, which can be associated with weathering of primary magnetite. Mean annual precipitation is positively correlated with the frequency dependent magnetic behavior, which is the result of neoformation of ultrafine maghaemite. The mineralogical analyses verify our observations. The good correlation between magnetic properties and mineralogy shows that the cheap and quick measurements of magnetic susceptibility can be used to estimate soil development.