Sulfuric materials
If Hypersulfidic material is exposed to atmospheric oxygen following drainage or exposure, iron sulfides within it become unstable and generate sulfuric acid and hence form Sulfuric material. The soil material becomes extremely acidic (pH 4 or less) and is also known as actual acid sulfate soil. Pale yellow mottles of the mineral jarosite are common and it is commonly underlain by hypersulfidic material. Note that not all sulfuric material will exhibit jarosite. Associated drainage waters may also be acidified and vegetation is often stained red with iron rich minerals.
Sulfuric material in profile
Photo credit: Queensland Department of Resources
On disturbed sites, excavated sulfuric materials may show the telltale signs of pale yellow jarosite and extreme concrete corrosion.
Photo credit: Bernie Powell
Link to an example of sulfuric material and iron staining