IAB meteorites are a group of

iron meteorite Iron meteorites, also called siderites or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron me ...

s according to their overall composition and a group of primitive achondrites because of silicate inclusions that show a strong affinity to winonaites and

chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar Syste ...

Description

The IAB meteorites are composed of

meteoric iron Meteoric iron, sometimes meteoritic iron, is a native metal and early-universe protoplanetary-disk remnant found in meteorites and made from the elements iron and nickel, mainly in the form of the mineral phases kamacite and taenite. Meteoric ...

(

kamacite Kamacite is an alloy of iron and nickel, which is found on Earth only in meteorites. According to the International Mineralogical Association (IMA) it is considered a proper nickel-rich variety of the mineral native iron. The proportion iron:ni ...

and

taenite Taenite is a mineral found naturally on Earth mostly in iron meteorites. It is an alloy of iron and nickel, with a chemical formula of and nickel proportions of 20% up to 65%. The name is derived from the Greek ταινία for "band, ribbo ...

) and silicate inclusions. Structurally they can be

hexahedrite Hexahedrites are a structural class of iron meteorite. They are composed almost exclusively of the nickel–iron alloy kamacite and are lower in nickel content than the octahedrites. The nickel concentration in hexahedrites is always below 5.8% ...

s, fine to coarse octahedrites, or even ataxites. Most of them are

octahedrite Octahedrites are the most common Iron meteorite#Structural classification, structural class of iron meteorites. The structures occur because the meteoric iron has a certain nickel concentration that leads to the exsolution of kamacite out of tae ...

with medium to coarse

-lamella and distinct

Widmanstätten pattern Widmanstätten patterns (), also known as Thomson structures, are figures of long Phase (matter), phases of nickel–iron, found in the octahedrite shapes of iron meteorite crystals and some pallasites. Iron meteorites are very often formed ...

ing. The silicate inclusions are composed of low-Ca

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

, high-Ca

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

troilite Troilite () is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe(1−x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency ...

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

, different phosphates,

and traces of

daubréelite Daubréelite is a rare sulfide mineral. It crystallizes with Cubic crystal system, cubic symmetry and has chemical composition of Fe2+Cr3+2S4. It usually occurs as black platy aggregates. Naming and history Daubréelite was named after the Frenc ...

and

chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of Iron, FeChromium, Cr2Oxygen, O4. It is an oxide mineral belonging to the spinel group. The ...

. This composition is very similar to the composition of winonaites, and it is therefore argued that the two groups share the same parent body. There are also similarities with the IIICD meteorites, but it is not yet clear whether they are also part of that parent body.

Classification

The IAB group was created from the older IA and IB groups. Some authors also prefer to call it IAB complex. There are numerous subdivisions of the IAB group: *IAB main group *sLL subgroup *sLM subgroup (originally IIIC) *sLH subgroup (originally IIID) *sHL subgroup *sHH subgroup (includes Gay Gulch trio) *Udei Station grouplet *Pitts grouplet *Algarrabo duo *Mundrabilla duo *Britstown duo *NWA 468 duo *Twin City duo *solo irons related to IAB *IAB related?

Parent body

Most scientists believe that the winonaites and the IAB meteorites share the same parent body. It is not yet fully understood whether the IIICD meteorites also belong to that body.

Notable specimen

* Canyon Diablo *Pitts meteorite (part of Pitts grouplet) *Udei station meteorite (part of Udei station grouplet) * Goose Lake Meteorite * Monturaqui * Nantan meteorite * Mörigen Arrowhead

References

{{meteorites Achondrite meteorites

Description

Classification

Parent body

Notable specimen

See also

References