Acid mine drainage in the context of Rio Tinto (river)

Arsenopyrite (IMA symbol: Apy) is an iron arsenic sulfide (FeAsS). It is a hard (Mohs 5.5–6) metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1.

When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it produces sulfur and arsenic vapor. With 46% arsenic content, arsenopyrite, along with orpiment, is a principal ore of arsenic. When deposits of arsenopyrite become exposed to the atmosphere, the mineral slowly converts into iron arsenates. Arsenopyrite is generally an acid-consuming sulfide mineral, unlike iron pyrite which can lead to acid mine drainage.

A lithoautotroph is an organism that derives energy from reactions of reduced compounds of mineral (inorganic) origin. Two types of lithoautotrophs are distinguished by their energy source; photolithoautotrophs derive their energy from light, while chemolithoautotrophs (chemolithotrophs or chemoautotrophs) derive their energy from chemical reactions. Chemolithoautotrophs are exclusively microbes. Photolithoautotrophs include macroflora such as plants; these do not possess the ability to use mineral sources of reduced compounds for energy. Most chemolithoautotrophs belong to the domain Bacteria, while some belong to the domain Archaea. Lithoautotrophic bacteria can only use inorganic molecules as substrates in their energy-releasing reactions. The term "lithotroph" is from Greek lithos (λίθος) meaning "rock" and trōphos (τροφοσ) meaning "consumer"; literally, it may be read "eaters of rock." The "lithotroph" part of the name refers to the fact that these organisms use inorganic elements/compounds as their electron source, while the "autotroph" part of the name refers to their carbon source being CO₂. Many lithoautotrophs are extremophiles, but this is not universally so, and some can be found to be the cause of acid mine drainage.

Lithoautotrophs are extremely specific in their source of reduced compounds. Thus, despite the diversity in using inorganic compounds that lithoautotrophs exhibit as a group, one particular lithoautotroph would use only one type of inorganic molecule to get its energy. A chemolithotrophic example is anaerobic ammonia oxidizing bacteria (anammox), which use ammonia and nitrite to produce dinitrogen (N₂). Additionally, in July 2020, researchers reported the discovery of chemolithoautotrophic bacterial cultures that feed on the metal manganese after performing unrelated experiments and named their bacterial species Candidatus Manganitrophus noduliformans and Ramlibacter lithotrophicus.

Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe₃(SO₄)₂(OH)₆. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct during the purification and refining of zinc and is also commonly associated with acid mine drainage and acid sulfate soil environments.

The London Clay Formation is a marine geological formation of Ypresian (early Eocene Epoch, c. 54-50 million years ago) age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from the lower Eocene rocks indicate a moderately warm climate, the tropical or subtropical flora. Though sea levels changed during the deposition of the clay, the habitat was generally a lush forest – perhaps like in Indonesia or East Africa today – bordering a warm, shallow ocean.

The London Clay is a stiff bluish clay which becomes brown when weathered and oxidized. Nodular lumps of pyrite are frequently found in the clay layers. Pyrite was produced by microbial activity (sulfate reducing bacteria) during clay sedimentation. Once clay is exposed to atmospheric oxygen, framboidal pyrite with a great specific surface is rapidly oxidized. Pyrite oxidation produces insoluble brown iron oxyhydroxide (FeOOH) and sulfuric acid leading to the formation of relatively soluble gypsum (CaSO₄·2H₂O, calcium sulfate dihydrate). This latter is more soluble and mobile than iron oxides and can further recrystallize to form larger crystals sometimes called selenite (coming from the moon, but not related to selenium, although the etymology is the same), or "waterstones".