Related Experiment Video
Updated: Jul 16, 2026
09:31
Preparation of Authigenic Pyrite from Methane-bearing Sediments for In Situ Sulfur Isotope Analysis Using SIMS
Published on: August 31, 2017
Greigite: a true intermediate on the polysulfide pathway to pyrite
Stefan Hunger1, Liane G Benning
1Earth and Biosphere Institute, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK. s.hunger@earth.leeds.ac.uk
Geochemical Transactions
|March 23, 2007
Summary
Pyrite formation from iron monosulfide proceeds through mackinawite and greigite intermediates. This study used in situ synchrotron ED-XRD to reveal greigite as a key intermediate, with solid-state mechanisms governing pyrite formation kinetics.
Area of Science:
- Geochemistry
- Mineralogy
- Solid-state chemistry
Background:
- Pyrite (FeS2) formation in anoxic sediments is crucial but poorly understood due to oxygen-sensitive intermediates.
- Mackinawite (FeS) and greigite (Fe3S4) are proposed intermediates, yet their characterization is challenging.
Purpose of the Study:
- To elucidate the in situ transformation mechanisms of mackinawite to greigite and pyrite.
- To determine the kinetic parameters and reaction pathways under hydrothermal conditions.
Main Methods:
- Hydrothermal synchrotron-based energy dispersive X-ray diffraction (ED-XRD) for real-time analysis.
- High-resolution microscopy to observe solid-phase morphology changes.
- Application of the Eyring equation to determine activation parameters.
Main Results:
- Greigite (Fe3S4) is confirmed as a critical intermediate in the mackinawite (FeS) to pyrite (FeS2) transformation pathway.
- The transformation kinetics follow a zero-order rate law, consistent with a solid-state mechanism.
- Crystal morphology suggests growth via oriented aggregation of nanoparticulate precursors.
Conclusions:
- The study provides definitive evidence for greigite as an intermediate in pyrite formation.
- Solid-state mechanisms, supported by kinetic data and crystal morphology, govern the transformation.
- Activation entropy values align with a solid-state mechanism, despite unusual activation enthalpies.
Related Concept Videos
02:26Preparation and Reactions of Sulfides
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.
01:20Sulfur Assimilation
Sulfur is an essential element in biological systems, contributing to synthesizing key biomolecules, including amino acids such as cysteine and methionine, and cofactors such as coenzyme A and biotin. Microorganisms primarily assimilate sulfur as sulfate (SO₄²⁻) from the environment, which must undergo a series of biochemical transformations before it can be incorporated into cellular components. As sulfate is highly oxidized, it must undergo assimilatory sulfate reduction to become...
01:29Microbes and the Sulfur Cycle
Sulfur is a vital element in Earth's biogeochemical systems. It transitions through various inorganic states, including sulfate (SO₄²⁻), elemental sulfur (S⁰), and sulfide (S²⁻). Abiotic and biological mechanisms across oxic and anoxic environments intricately mediate these transformations. Sulfate, the most oxidized form of sulfur, is predominantly stored in rocks, marine sediments, and oceanic waters, acting as a long-term reservoir in the global sulfur cycle.In oxic environments,...
01:19Acid Mine Drainage
Mining activities that disturb sulfide-rich rocks, particularly those containing pyrite (FeS₂), initiate a cascade of geochemical and microbiological processes with serious environmental implications. When exposed to air and water, pyrite undergoes oxidation, releasing sulfate, ultimately forming sulfuric acid and mobilizing heavy metals into surrounding water systems. This phenomenon, known as acid mine drainage (AMD), results in low pH waters laden with toxic elements that threaten aquatic...
03:45Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
01:27Microbial Leaching
Microbial leaching, also known as bioleaching, is an environmentally favorable method for extracting metals from low-grade ores using specific microorganisms. This biotechnological approach is particularly valuable for mining operations targeting copper, gold, and uranium, where traditional extraction methods may be economically or environmentally impractical.Copper Leaching and Microbial CatalysisIn copper bioleaching, crushed ore is arranged into heaps and irrigated with a dilute sulfuric...