text: The terms ‘sulfidic material’ and ‘sulfuric material’ were primarily coined by Prof Delvin Fanning (University of Maryland), Prof Martin Rabenhorst (University of Maryland), and Prof Rob Fitzpatrick (University of Adelaide) – and have been incorporated into the Australian Soil Classification (ASC) and World Reference Base (WRB) as diagnostic features of soil. For example, under the ASC, a Sulfuric Extratidal Hydrosol would refer to a soil that is saturated for 2-3 months of the year (i.e., a Hydrosol), located in an extratidal setting, and which contains sulfuric material. Therefore, acid sulfate soils may be described more technically as soils that contain sulfidic and/or sulfuric material. 
  Sulfuric material refers to soil material that has a pH of less than 4 owing to the oxidation of sulfidic material. 
  Sulfidic material refers to “soil materials containing detectable inorganic sulfides (≥0.01% sulfidic sulfur) that can exist as horizons or layers at least 30 mm thick or as surficial features”, and is further divided into 3 classes: hyposulfidic, hypersulfidic, and monosulfidic. 
  Conceptually, hyposulfidic and hypersulfidic materials are used to distinguish between sulfidic material that, respectively, would not and would experience a drop in pH to below 4 if exposed to prevailing oxidising conditions. By definition, hyposulfidic material does not convert to sulfuric material upon oxidation. 
  In contrast to both hyposulfidic and hypersulfidic materials, monosulfidic material contains high concentrations of detectable monosulfides (≥ 0.01% acid volatile sulfide) (e.g., greigite and mackinawite). Note that monosulfidic material has not replaced Monosulfidic Black Ooze (MBO), which is now considered a type of monosulfidic material.
  The terms ‘sulfidisation’ and ‘sulfuricisation’ were coined to refer to the formation of sulfidic and sulfuric material, respectively. Although the terms have not been formally adopted in the ASC, their use is encouraged in Australia. However, the terms should not be used synonymously with other terms that also refer to the formation or transformation of sulfides (e.g., pyritization). Similarly, sulfidic material should not be used interchangeably with similar terms such as pyritic/sulfidic sediment, rock and regolith, which may be found in publications on Acid Rock systems. The broad term sulfidic geomedia could be used to refer to both sulfidic material and pyritic/sulfidic sediment, rock and regolith; but it has no formal definition in Australia and should not be used in lieu of sulfidic material.