Mineralogy, chemistry, and some magnetic properties of altered basaltic rocks from DSDP Site 396B are rather simply related to one another but differ dramatically with the nature of the igneous material and with the sharp alteration zonation within individual basalt fragments. Low-temperature alteration of the major igneous minerals appears to have been primarily a function of oxidation, which effects titanomagnetic pervasively (gray interiors) and olivine locally (brown zones). Destruction of olivine in the pillow basalts released Mg++, SiO2, Co, and Ni to the circulating solution and resulted in a calculated 9--10% decrease in density of the most altered (brown) zones in the rock. Seawater phosphate was incorporated in secondary ferric oxides replacing the olivine. In the massive basalts, all of the SiO2 and much of the Mg from olivine recombined as smectite, and the inferred rock density is almost unchanged. In almost all of the crystalline rocks, primary Ca, Na, Fe, Ti, and Al were immobile, owing to the metastability of plagioclase and clinopyroxene. The filling of cracks by smectite, Fe--Mn oxides, phillipsite, and calcite consumed elements from various sources and was probably more important than basalt alteration for some chemical fluxes. Values of Δ18O for the altered rocks are roughly 1--3%0 higher than their fresh equivalents, owing to the addition of 18O-rich secondary oxides, smetites, and lesser carbonates and phillipsite. The highest values are associated with the smetite-rich samples. However Δ18O is not a good indicator of the degree of alteration because of strong leaching in the most altered zones of the pillow basalts. Pervasive oxidation of titanomaghemite to titanomaghemite has caused all samples to have high Curie temperatures, indicating up to about 70%oxidation. With the destruction of olivine in the brown zones, strong oxidation has caused breakdown of titanomaghemite to more stable nonmagnetic oxides, hence a drop in saturation intensity. These reactions have proceeded further in the pillow basalts than in the massive basalts. Freshly created oceanic crust consisting of various basaltic materials with abundant void space and (or) interstitial sediments is clearly heterogeneous; this primary heterogeneity is accentuated by alteration.