Editing Kamacite (section)

==Chemistry==

===Formula and dominant elements===
Kamacite is made up of a repeating unit of α-(Fe, Ni), {{chem|Fe|0.9|Ni|0.1}}, in which both iron and nickel have the valence zero (Fe<sup>0</sup> and Ni<sup>0</sup>) as they are metallic native elements commonly found in iron meteorites. Besides trace elements, it is normally considered to be made up of 90% iron and 10% nickel but can have a ratio of 95% iron and 5% nickel. This makes iron the dominant element in any sample of kamacite. It is grouped with the native elements in both Dana and Nickel-Strunz classification systems.<ref name="Ramsden"/>

===Conditions of formation===
Kamacite starts to form around 723&nbsp;°C, where iron splits from being [[Crystal structure|face centered to body centered]] while nickel remains face centered. To accommodate this areas start to form of higher iron concentration displacing nickel to the areas around it which creates taenite which is the nickel end member.

===Trace elements===
There has been a great deal of research into kamacite's trace elements. The most notable trace elements in kamacite are [[gallium]], [[germanium]], [[cobalt]], [[copper]], and [[chromium]]. Cobalt is the most notable of these where the [[nickel]] content varies from 5.26% to 6.81% and the cobalt content can be from 0.25% to 0.77%.<ref>{{cite journal |last1=Nichiporuk |first1=W. |title=Variations in the content of nickel, gallium, germanium, cobalt, copper and chromium in the kamacite and taenite phases of iron meteorites |journal=Geochimica et Cosmochimica Acta |year=1957 |volume=13 |issue=4 |pages=233–236 |doi=10.1016/0016-7037(58)90025-5|bibcode=1958GeCoA..13..233N }}</ref> All of these trace elements are metallic and their appearance near the kamacite taenite border can give important clues to the environment the meteorite was formed in. [[Mass spectrometry]] has revealed kamacite to contain considerable amounts of [[platinum]] to be an average of 16.31 (μg/g), [[iridium]] to be an average of 5.40 (μg/g), [[osmium]] to be an average of 3.89 (μg/g), [[tungsten]] to be an average of 1.97 (μg/g), [[gold]] to be an average of 0.75 (μg/g), and [[rhenium]] to be an average of 0.22 (μg/g).<ref>{{cite journal |last1=Rasmussen |first1=K. |last2=Greenway |first2=T. |last3=Gwozdz |first3=R. |title=The composition of kamacite in iron meteorites investigated by accelerator mass spectroscopy, neutron activation analysis and analytical electron microscopy |journal=Nuclear Instruments and Methods in Physics Research |volume=36 |issue=1 |pages=43 |year=1989|bibcode=1989NIMPB..36...43R |doi=10.1016/0168-583X(89)90058-X }}</ref> The considerable amounts of cobalt and platinum are the most notable.

===Important minor elements, substitutions, solid solutions===
Kamacite sulfurization has been done experimentally in laboratory conditions. Sulfurization resulted in three distinct phases: a mono-sulfide [[solid solution]] ({{chem|Fe|x|(Ni,Co)|1-x|S}}), a pentlandite phase ({{chem|Fe|x|(Ni,Co)|9-x|S|8}}), as well as a P-rich phase. This was done in a lab to construct conditions concurrent with that of the solar nebula. With this information it would be possible to extract information about the thermodynamic, kinetic, and physical conditions of the early solar system. This still remains speculatory as many of the sulfides in meteorites are unstable and have been destroyed.<ref>{{cite journal |last1=Lauretta |first1=D. |title=Kamacite sulfurization in the solar nebula |journal=Meteoritics & Planetary Science |year=1998 |volume=33 |issue=4 |page=4 |doi=10.1111/j.1945-5100.1998.tb01689.x|bibcode=1998M&PS...33..821L |doi-access= }}</ref> Kamacite also alters to [[tochilinite]] ({{chem|Fe|2+| · 5-6 (Mg, Fe|2+|)|5|S|6|(OH)|10}}). This is useful for giving clues as to how much the meteorite as a whole has been altered. Kamacite to tochilinite alteration can be seen in petrologic microscopes, scanning electron microscope, and electron microprobe analysis. This can be used to allow researchers to easily index the amount of alteration that has taken place in the sample. This index can be later referenced when analyzing other areas of the meteorite where alteration is not as clear.<ref>{{cite journal |last1=Palmer |first1=E. E. |title=A kamacite alteration index for CM chondrites |journal=41st Lunar and Planetary Science Conference |issue=1533 |pages=2211 |year=2010|bibcode=2010LPI....41.2211P }}</ref>

===Relationship with taenite===
[[Taenite]] is the nickel rich end member of the kamacite–taenite solid solution. Taenite is naturally occurring on Earth whereas kamacite is only found on Earth when it comes from space. Kamacite forms taenite as it forms and expels nickel to the surrounding area, this area forms taenite. Due to the face centered nature of the kamacite lattice and the body centered nature of the nickel lattice the two make intricate angles when they come in contact with each other. These angles reveal themselves macroscopically in the Thomson structure. Also due to this relationship we get the terms ataxite, hexahedrites and octahedrite. [[Ataxite]] refers to meteorites that do not show a grossly hexahedral or octahedral structure. Meteorites composed of 6 wt% or less nickel are often referred to as hexahedrites due to the crystal structure of kamacite being isometric and causing the meteorite to be cubic. Likewise if the meteorite is dominated by the face centered taenite it is called an octahedrite as kamacite will exsolve from the octahedral crystal boundaries of taenite making the meteorite appear octahedral. Both hexahedrites and octahedrite only appear when the meteorite breaks along crystal planes or when prepared to accentuate the Thomson structures therefore many are mistakenly called ataxites ar first.<ref name="Goldstein" /><ref name="Norton p75-111">{{cite book |last1=Norton |first1=O. R. |title=Field Guide to Meteors and Meteorites Patrick Moore's Practical Astronomy Series |year=2008 |publisher=Springer |location=The Chondrites |pages=75–111}}</ref>

===Stability range===
Kamacite is only stable at temperatures below 723&nbsp;°C <ref name="Goldstein" /> or 600&nbsp;°C (Stacey and Banerjee, 2012),<ref name="Stacey_Banerjee_2012" /> as that is where iron becomes cool enough to arrange in a body centered crystal structure. Kamacite is also only stable at low pressures as can be assumed because it only forms in the [[outer space|space]].<ref name="Goldstein" />

===Effect of shock===
[[Metallography|Metallographic]] and [[X-ray diffraction]] can be used on kamacite to determine the shock history of a meteorite. Using hardness to determine shock histories has been experimented with but was found to be too unreliable. Vickers hardness test was applied to a number of kamacite samples and shocked meteorites were found to have values of 160–170&nbsp;kg/mm and non-shocked meteorites can have values as high as 244&nbsp;kg/mm.<ref name="Jain Gordon Lipschutz" /> Shock causes a unique iron transformation structure that is able to be measured using metallographic and X-ray diffraction techniques. After using metallographic and X-ray diffraction techniques to determine shock history it was found that 49% of meteorites found on Earth contain evidence of shock.