This paper explores soil mineralogy across the land/sea boundary in the Mid-Atlantic region and points out that the parent materials of many upland soils in the region accumulated as sediments or subaqueous soils under estuarine or marine conditions. Geologic sediments and sedimentary/metamorphic rocks in the region contain iron sulfides, mainly pyrite, that upon oxidation leave a strong imprint upon the mineralogy and other properties of post-active acid sulfate soils formed on these materials. One aspect is the Fe and S mineralogy of potential acid sulfate soils in tidal marsh and subaqueous soils vs. that of active and post-active upland soils. Iron (hydr)oxide minerals are converted into iron sulfides with S coming from sulfate in sea water in the marsh and subaqueous soils where sulfidization is active -- in part by reaction with soluble sulfide as demonstrated by the rapid formation of iron sulfides from iron (hydr)oxides introduced into these environments. Upon exposure to oxidizing conditions, e.g. in upland DM (dredged materials) deposition sites, the Fe sulfides are rapidly converted back into iron (hydr)oxides and sulfates, some of which (especially jarosite, with time of formation possibly dateable by argon isotopic methods) are retained into the post-active stage to demonstrate that sulfuricization was once active in upland Ultisols. The paper will also consider the silicate mineralogy in the various environments – e.g. how glauconite formed in marine subaqueous environments in the geologic past, leaving almost no inherited/detrital phyllosilicates in some Eocene and Upper Cretaceous sediments – reminding us of the possibility of glauconitization in sea water-affected subaqueous soils/sediments with potassium from sea water incorporated into silicates, mimicking the S of sulfate that is transformed into sulfide minerals in these environments. On the other hand, in uplands the acidity in active acid sulfate soil situations apparently releases silica and other elements from silicates into solution with silica re-precipitation into opal-CT and probably other silicate minerals, perhaps catalyzed by higher pH when high ionic strength soil solutions, generated in active acid sulfate zones, percolate into underlying calcareous zones etc. Plinthite/ironstone and duripan-like features in some upland soils of the region likely have formed by sulfuricization. We shall also consider carbonate minerals/gypsum relationships – the carbonate shells deposited in the subaqueous environments and gypsum that forms from the dissolution of shell beds in uplands during sulfuricization.