Mineral Composition: Iron Mineralogy

Iron minerals occur in many forms and can be imlicated as being related to life and living processes in a variety of environments.

Magnetite (Fe3O4) is a mangetic mineral with mixed oxidation states of iron that is used in biology for magnetotaxis. The presence and purity of magnetite in certain samples may implicate potential biogenicity.

Created at: 
2021-01-11
Updated at: 
2023-03-16
Curator: 
Svetlana Shkolyar
Authors: 
Stan Gliniewicz , Svetlana Shkolyar , Tatiana Gibson , Holden Faraday  
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Definition
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Magnetite chemical purity is predominantly achieved by biological processes. [General]

Environments
Mars: Surface
eThe magnetite observed in martian meteorite ALH84001 resembles chemically pure terrestrial magnetite produced by magnetotactic bacteria rather than the chemically impure magnetite produced through inorganic processes.

eMagnetotactic bacteria produce chemically pure magnetite in the form of magnetosomes, intracellular accumulations of magnetite that can be preserved as fossils. 

e

Chemically pure magnetite is indicative of biological processes because even when cultured in a medium with impurities, magnetotactic bacteria will still precipitate chemically pure magnetite.


 
 

Chemical purity should not be used as the sole distinguisher between abiotic and biological magnetite. [General]

Environments
Mars: Surface
eChemically pure magnetite has been synthesized in laboratory settings, indicating that biotic processes are not the only means to generate high purity levels.

e

Chemically pure magnetite such as that observed in ALH84001 can be produced abiotically through a meteoric impact that sufficiently raises temperature and pressure conditions.


eMagnetotactic bacteria cultured in a medium with high impurity concentrations can precipitate impure magnetite.

Definition
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Definition
HIGH
LOW
 

Chemically pure magnetite crystals are usually not produced abiotically because natural impurities are usually incorporated in the crystal lattice during their formation. [Congruence]

Environments
All
eThe formation of abiotic magnetite will almost always be in the presence of other elements, and the elemental partition coefficients will be higher in abiotically formed magnetite. 

Definition
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LOW