<p>First, a correction. A <a href="https://en.wikipedia.org/wiki/Solid_solution" rel="nofollow noreferrer">solid solution</a> is between different compositions in the same phase. For example, olivine is a solid solution of forsterite (Mg<sub>2</sub>SiO<sub>4</sub>) and fayalite (Fe<sub>2</sub>SiO<sub>4</sub>).</p>
<p>There are two common iron–nickel alloys found in meteorites (pallasites and others): kamacite and taenite. They are commonly intergrown into lamallae called &quot;Widmanstätten pattern&quot;. It looks like this:</p>
<p><a href="https://i.sstatic.net/BEQIm.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/BEQIm.jpg" alt="enter image description here" /></a></p>
<p>Kamacite has up to about 10% nickel, whereas taenite can get up to ~60% nickel, but commonly found up to 30%.</p>
<p>Kamacite has the space group Im3m, making it hexoctahedral body-centered. Taenite has the space group Fm3m, making it hexoctahedral face-centered.</p>

CC BY-SA 3.0
2018-02-12T23:16:20.267Z
2018-02-12T23:16:20.267Z
2020-06-18T08:25:19.090Z
Gimelist
<p>The metallic part ( essentially all two elements= Iron + nickel) is two phases mixed together : Body Centered Cubic - magnetic, and Face Centered Cubic - nonmagnetic. So the answer to your question is that it is both .  Iron ( BCC) starts to form FCC when Ni exceeds 6 %. The proverbial 18 - 8 stainless steel is 8 % Ni and generally non magnetic austenite phase. My educated guess is the classic  Widmidststten pattern is ferrite ( BCC ) grains/crystals forming from the original austenite ( FCC ) grains/crystals. But it is not that simple as when hot ( 1500 F ) it is 100 % austenite ( FCC ). Further complication is the austenite ( FCC , nickel rich) makes crystal twins . The twins can also give the Widmanstratten structure. And more complicated because temperature history can also affect the FCC / BCC morphology.  [ Maybe I cheated but I searched meteors on the net and learned some but also found some mistakes in the references. ] </p>

CC BY-SA 3.0
2018-02-13T08:24:44.263Z
The Widmanstattten pattern is due to exolution of taenite and kamacite.
bon
CC BY-SA 3.0
2018-02-14T21:07:31.313Z
Taenite and kamacite are the mineral  names for austenite  and ferrite ; aka , FCC and BCC.
blacksmith37
CC BY-SA 3.0
2018-02-13T01:42:01.350Z
2018-02-13T01:42:01.350Z
blacksmith37
<p>I have recently been learning and researching about meteorite types and classification. Pallasites are mainly composed of a 'solid-solution' of olivine crystals and an iron-nickel alloy. My question is: what is the phase of the iron-nickel alloy, in a body-centered cubic crystal structure (alpha-iron, and hexahedrites) or face-centered cubic?</p>

<geochemistry><mineralogy><meteorite><crystallography>
Iron-nickel phase in pallasite meteorites
PlanetGazer8360
# Iron-nickel phase in pallasite meteorites

(Asked by: username_0 on 2018-02-12)

I have recently been learning and researching about meteorite types and classification. Pallasites are mainly composed of a 'solid-solution' of olivine crystals and an iron-nickel alloy. My question is: what is the phase of the iron-nickel alloy, in a body-centered cubic crystal structure (alpha-iron, and hexahedrites) or face-centered cubic?

**Tags:** geochemistry, mineralogy, meteorite, crystallography


---

## 2 answers

### Answer by username_1 on 2018-02-12. Score: 2 | Accepted answer

First, a correction. A [solid solution](https://en.wikipedia.org/wiki/Solid_solution) is between different compositions in the same phase. For example, olivine is a solid solution of forsterite (Mg2SiO4) and fayalite (Fe2SiO4).

There are two common iron–nickel alloys found in meteorites (pallasites and others): kamacite and taenite. They are commonly intergrown into lamallae called "Widmanstätten pattern". It looks like this:

[![enter image description here](https://i.sstatic.net/BEQIm.jpg)](https://i.sstatic.net/BEQIm.jpg)

Kamacite has up to about 10% nickel, whereas taenite can get up to ~60% nickel, but commonly found up to 30%.

Kamacite has the space group Im3m, making it hexoctahedral body-centered. Taenite has the space group Fm3m, making it hexoctahedral face-centered.


---

### Answer by username_2 on 2018-02-13. Score: -1

The metallic part ( essentially all two elements= Iron + nickel) is two phases mixed together : Body Centered Cubic - magnetic, and Face Centered Cubic - nonmagnetic. So the answer to your question is that it is both . Iron ( BCC) starts to form FCC when Ni exceeds 6 %. The proverbial 18 - 8 stainless steel is 8 % Ni and generally non magnetic austenite phase. My educated guess is the classic Widmidststten pattern is ferrite ( BCC ) grains/crystals forming from the original austenite ( FCC ) grains/crystals. But it is not that simple as when hot ( 1500 F ) it is 100 % austenite ( FCC ). Further complication is the austenite ( FCC , nickel rich) makes crystal twins . The twins can also give the Widmanstratten structure. And more complicated because temperature history can also affect the FCC / BCC morphology. [ Maybe I cheated but I searched meteors on the net and learned some but also found some mistakes in the references. ]

> **Comments:**
> **username_3**: The Widmanstattten pattern is due to exolution of taenite and kamacite.  
> **username_2**: Taenite and kamacite are the mineral  names for austenite  and ferrite ; aka , FCC and BCC.  

---

