IAB meteorites are a group of
iron meteorite
Iron meteorites, also known as 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 ...
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 differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form p ...
s.
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 ir ...
(
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: ...
and
taenite) and silicate inclusions. Structurally they can be
hexahedrites, fine to coarse
octahedrites, or even
ataxites.
Most of them are
octahedrite
Octahedrites are the most common 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 taenite while cooling.
Structure
Octahedr ...
with medium to coarse
taenite-lamella and distinct
Widmanstätten pattern
Widmanstätten patterns, also known as Thomson structures, are figures of long nickel–iron crystals, found in the octahedrite iron meteorites and some pallasites. They consist of a fine interleaving of kamacite and taenite bands or ribbons ...
ing.
The silicate inclusions are composed of low-Ca
pyroxene, high-Ca
pyroxene,
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
,
plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...
,
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 whic ...
,
graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...
, different phosphates,
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 ir ...
and traces of
daubréelite and
chromite.
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
The Goose Lake meteorite is a meteorite that was found at Goose Lake in the United States by two hunters from Oakland, California on October 13, 1938.
In 1939 it was acquired by the United States National Museum. From 1939 until January 14, 1 ...
*
Monturaqui
*
Nantan meteorite
See also
*
Glossary of meteoritics
This is a glossary of terms used in meteoritics, the science of meteorites.
#
* 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites.
* 4 Vesta – second-largest asteroid in the asteroid b ...
References
{{meteorites
Achondrite meteorites