Nontronite forms from the weathering of biotite and basalts, precipitation of iron and silicon rich hydrothermal fluids and in deep sea hydrothermal vents.
Weathering is usually confined to the top few meters of geologic material, because physical, chemical, and biological stresses generally decrease with depth.
Conditions for the formation of deeply weathered regolith include a topographically moderate relief flat enough to allow leaching of the products of chemical weathering.
Beneath the surface layer of unsorted glacial till are strata of sandstone and ironstone which weathering and erosion have exposed above the surface in areas.
The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects.
This magnetic field may be deflecting particles from the solar wind, and thus preventing the underlying surface from growing darker because of space weathering.
