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Iron meteorites, also known as
siderite :''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of ...

siderite
s, or
ferrous In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...
meteorites, are a type of
meteorite A meteorite is a solid piece of debris from an object, such as a comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces ...
that consist overwhelmingly of an
iron–nickel alloy An iron–nickel alloy or nickel–iron alloy, abbreviated FeNi or NiFe, is a group of alloys consisting primarily of the chemical element, elements nickel (Ni) and iron (Fe). It is the main constituent of the "iron" planetary cores and iron meteor ...
known as
meteoric iron Meteoric iron, sometimes meteoritic iron, is a native metal A native metal is any metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractu ...
that usually consists of two
mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...

mineral
phases:
kamacite Kamacite is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appea ...
and
taenite 200px, Widmanstätten pattern showing the two forms of Nickel-Iron, Kamacite and Taenite, in an octahedrite meteorite Taenite (Fe, Ni) is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-log ...
. Most iron meteorites originate from cores of
planetesimal 486958 Arrokoth, the first pristine planetesimal visited by a spacecraft. Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to fo ...
s, with the exception of the IIE iron meteorite group The iron found in iron meteorites was one of the earliest sources of usable iron available to
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

human
s, due to the malleability and ductility of the meteoric iron, before the development of
smelting Smelting is a process of applying heat to ore ore – psilomelane (size: 6.7 × 5.8 × 5.1 cm) ore – galena and anglesite (size: 4.8 × 4.0 × 3.0 cm) ore (size: 7.5 × 6.1 × 4.1 cm) File:OreCartPachuca.JPG, upMinecart on ...
that signaled the beginning of the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the ...
.


Occurrence

Although they are fairly rare compared to the
stony meteorite A meteorite classification system attempts to group similar meteorite, meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especi ...
s, comprising only about 5.7% of witnessed falls, iron meteorites have historically been heavily over-represented in
meteorite A meteorite is a solid piece of debris from an object, such as a comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces ...
collections. This is due to several factors: * They are easily recognized as unusual even by laymen, as opposed to stony meteorites. Modern-day searches for meteorites in deserts and Antarctica yield a much more representative sample of meteorites overall. * They are much more resistant to weathering. * They are much more likely to survive atmospheric entry, and are more resistant to the resulting
ablation Ablation is removal or destruction of material from an object by vaporization, chipping, or other erosive processes. Examples of ablative materials are described below, and include spacecraft 275px, The US Space Shuttle flew 135 times from ...
. Hence, they are more likely to be found as large pieces. * They can be found even when buried by use of surface metal detecting equipment, due to their metallic composition. Because they are also denser than stony meteorites, iron meteorites also account for almost 90% of the mass of all known meteorites, about 500 tons. All the largest known meteorites are of this type, including the largest—the
Hoba meteorite The Hoba ( ) meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural s ...
.


Origin

Iron meteorites have been linked to
M-type asteroid M-type asteroids are asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc i ...
s because both have similar spectral characteristics in the visible and near-infrared. Iron meteorites are thought to be the fragments of the cores of larger ancient
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observ ...

asteroid
s that have been shattered by impacts. The heat released from the radioactive decay of the short-lived nuclides 26Al and 60Fe is considered as a plausible cause for the melting and differentiation of their parent bodies in the early Solar System. Melting produced from the heat of impacts is another cause of melting and differentiation. The IIE iron meteorites may be a notable exception, in that they probably originate from the crust of
S-type asteroid S-type asteroids are asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc i ...
6 Hebe Hebe (minor planet designation: 6 Hebe) is a large asteroid belt, main-belt asteroid, containing around 0.5% of the mass of the belt. However, due to its apparently high bulk density (greater than that of the Moon or even Mars), Hebe does not ran ...

6 Hebe
. Chemical and isotope analysis indicates that at least about 50 distinct parent bodies were involved. This implies that there were once at least this many large, differentiated, asteroids in the asteroid belt – many more than today.


Composition

The overwhelming bulk of these meteorites consists of the FeNi-alloys
kamacite Kamacite is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appea ...
and
taenite 200px, Widmanstätten pattern showing the two forms of Nickel-Iron, Kamacite and Taenite, in an octahedrite meteorite Taenite (Fe, Ni) is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-log ...
. Minor minerals, when occurring, often form rounded nodules of
troilite Troilite is a rare iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the period ...
or
graphite Graphite (), archaically referred to as plumbago, is a crystalline form of the element carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table ...

graphite
, surrounded by
schreibersite Schreibersite is generally a rare iron nickel phosphide mineral, , though common in iron-nickel meteorites. It has been found on Disko Island in Greenland and Illinois. Another name used for the mineral is rhabdite. It forms tetragonal crystals wi ...
and
cohenite Cohenite is a naturally occurring iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 ...
.
Schreibersite Schreibersite is generally a rare iron nickel phosphide mineral, , though common in iron-nickel meteorites. It has been found on Disko Island in Greenland and Illinois. Another name used for the mineral is rhabdite. It forms tetragonal crystals wi ...
and
troilite Troilite is a rare iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the period ...
also occur as plate shaped inclusions, which show up on cut surfaces as cm-long and mm-thick lamellae. The
troilite Troilite is a rare iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the period ...
plates are called ''
Reichenbach
Reichenbach
lamellae''. The chemical composition is dominated by the elements
Fe
Fe
,
Ni
Ni
and
Co
Co
, which make up more than 95%.
Ni
Ni
is always present; the concentration is nearly always higher than 5% and may be as high as about 25%. A significant percentage of nickel can be used in the field to distinguish meteoritic irons from man-made iron products, which usually contain lower amounts of Ni, but it is not enough to prove meteoritic origin.


Use

Iron meteorites were historically used for their
meteoric iron Meteoric iron, sometimes meteoritic iron, is a native metal A native metal is any metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractu ...
, which was forged into cultural objects, tools or weapons. With the advent of smelting and the beginning of the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the ...
the importance of iron meteorites as a resource decreased, at least in those cultures that developed those techniques. In Ancient Egypt and other civilizations before the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the ...
, iron was as valuable as gold, since both came from meteorites, for example
Tutankhamun's meteoric iron dagger Tutankhamun's meteoric iron dagger, also known as Tutankhamun's iron dagger and King Tut's dagger, is an iron-bladed dagger discovered during 1925 in the ancient Egyptian Pharaoh Tutankhamun's 14th century BC KV62, King's Valley tomb by archaeolog ...
. The Inuit used the
Cape York meteorite The Cape York meteorite, also known as the Innaanganeq meteorite, is one of the largest known iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel a ...
for a much longer time. Iron meteorites themselves were sometimes used unaltered as collectibles or even religious symbols (e.g. Clackamas worshiping the
Willamette meteorite The Willamette Meteorite, officially named WillametteMeteoritical Bulletin ...

Willamette meteorite
). Today iron meteorites are prized collectibles for academic institutions and individuals. Some are also tourist attractions as in the case of the
Hoba meteorite The Hoba ( ) meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural s ...
.


Classification

Two classifications are in use: the classic structural classification and the newer chemical classification.


Structural classification

The older structural classification is based on the presence or absence of the
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 ca ...
, which can be assessed from the appearance of polished cross-sections that have been etched with acid. This is connected with the relative abundance of nickel to iron. The categories are: *
Hexahedrite Hexahedrites are a structural class of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of tw ...
s (H): low nickel, no
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 ca ...
, may present
Neumann lines Neumann lines, or Neumann bands, are fine patterns of parallel lines seen in cross-sections of many hexahedrite iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly o ...
; *
Octahedrite Octahedrites are the most common structural class of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usua ...
s (O): average to high nickel,
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 ca ...
s, most common class. They can be further divided up on the basis of the width of the kamacite lamellae from coarsest to finest. **Coarsest (Ogg): lamellae width > 3.3 mm **Coarse (Og): lamellae width 1.3–3.3 mm **Medium (Om): lamellae width 0.5–1.3 mm **Fine (Of): lamellae width 0.2–0.5 mm **Finest (Off): lamellae width < 0.2 mm **Plessitic (Opl): a transitional structure between octahedrites and ataxites *
Ataxite Ataxites (from Greek meaning "without structure") are a structural class of iron meteorites with a high nickel content and show no Widmanstätten patterns upon etching. Characteristics Ataxites are composed mainly of meteoric iron, a native metal ...
s (D): very high nickel, no
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 ca ...
, rare.


Chemical classification

A newer chemical classification scheme based on the proportions of the trace elements
Ga
Ga
,
Ge
Ge
and
Ir
Ir
separates the iron meteorites into classes corresponding to distinct
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observ ...

asteroid
parent bodies. This classification is based on diagrams that plot
nickel Nickel is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

nickel
content against different trace elements (e.g. Ga, Ge and Ir). The different iron meteorite groups appear as data point clusters. There were originally four of these groups designated by the Roman numerals I, II, III, IV. When more chemical data became available these were split, e.g. Group IV was split into IVA and IVB meteorites. Even later some groups got joined again when intermediate meteorites were discovered, e.g. IIIA and IIIB were combined into the IIIAB meteorites. In 2006 iron meteorites were classified into 13 groups (one for uncategorized irons): * IAB ** IA: Medium and coarse octahedrites, 6.4-8.7% Ni, 55-100 ppm Ga, 190-520 ppm Ge, 0.6–5.5 ppm Ir, Ge-Ni correlation negative. ** IB: Ataxites and medium octahedrites, 8.7–25% Ni, 11–55 ppm Ga, 25–190 ppm Ge, 0.3-2 ppm Ir, Ge-Ni correlation negative. * IC: 6.1–6.8% Ni. The Ni concentrations are positively correlated with As (4–9 μg/g), Au (0.6–1.0 μg/g) and P (0.17–0.40%) and negatively correlated with Ga (54–42 μg/g), Ir (9–0.07 μg/g) and W (2.4–0.8 μg/g). * IIAB ** IIA: Hexahedrites, 5.3–5.7% Ni, 57–62 ppm Ga, 170–185 ppm Ge, 2-60ppm Ir. ** IIB: Coarsest octahedrites, 5.7–6.4% Ni, 446-59 pm Ga, 107–183 ppm Ge, 0.01–0.5 ppm Ir, Ge-Ni correlation negative. * IIC: Plessitic octahedrites, 9.3–11.5% Ni, 37–39 ppm Ga, 88–114 ppm Ge, 4–11 ppm Ir, Ge-Ni correlation positive * IID: Fine to medium octahedrites, 9.8–11.3%Ni, 70–83 ppm Ga, 82–98 ppm Ge, 3.5–18 ppm Ir, Ge-Ni correlation positive * IIE: octahedrites of various coarseness, 7.5–9.7% Ni, 21–28 ppm Ga, 60–75 ppm Ge, 1–8 ppm Ir, Ge-Ni correlation absent * IIIAB: Medium octahedrites, 7.1–10.5% Ni, 16–23 ppm Ga, 27–47 ppm Ge, 0.01-19 ppm Ir * IIICD: Ataxites to fine octahedrites, 10–23% Ni, 1.5–27 ppm Ga, 1.4–70 ppm Ge, 0.02–0.55 ppm Ir * IIIE: Coarse octahedrites, 8.2–9.0% Ni, 17–19 ppm Ga, 3–37 ppm Ge, 0.05-6 ppm Ir, Ge-Ni correlation absent * IIIF: Medium to coarse octahedrites, 6.8–7.8% Ni,6.3–7.2 ppm Ga, 0.7–1.1 ppm Ge, 1.3–7.9 ppm Ir, Ge-Ni correlation absent * IVA: Fine octahedrites, 7.4–9.4% Ni, 1.6–2.4 ppm Ga, 0.09–0.14 ppm Ge, 0.4-4 ppm Ir, Ge-Ni correlation positive * IVB: Ataxites, 16–26% Ni, 0.17–0.27 ppm Ga, 0,03–0,07 ppm Ge, 13–38 ppm Ir, Ge-Ni correlation positive * Ungrouped meteorites. This is actually quite a large collection (about 15% of the total) of over 100 meteorites that do not fit into any of the larger classes above, and come from about 50 distinct parent bodies. Additional groups and grouplets are discussed in the scientific literature: * IIG:
Hexahedrite Hexahedrites are a structural class of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of tw ...
s with coarse
schreibersite Schreibersite is generally a rare iron nickel phosphide mineral, , though common in iron-nickel meteorites. It has been found on Disko Island in Greenland and Illinois. Another name used for the mineral is rhabdite. It forms tetragonal crystals wi ...
.
Meteoric iron Meteoric iron, sometimes meteoritic iron, is a native metal A native metal is any metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractu ...
has low nickel concentration.


Magmatic and nonmagmatic (primitive) irons

The iron meteorites were previously divided into two classes: magmatic irons and non magmatic or primitive irons. Now this definition is deprecated.


Stony–iron meteorites

There are also specific categories for mixed-composition meteorites, in which iron and 'stony' materials are combined. * II) Stony–iron meteorites **
Pallasite The pallasites are a class of stony–iron meteorite. Structure and composition It consists of centimeter-sized olivine The mineral olivine () is a magnesium iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la ...
s *** Main group pallasites *** Eagle station pallasite grouplet *** Pyroxene Pallasite grouplet **
Mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, co ...
group


Gallery

File:Hoba Meteorite sire.jpg, The
Hoba meteorite The Hoba ( ) meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural s ...
, the biggest known iron meteorite. It lies in
Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa Southern Africa is the south South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east a ...

Namibia
and weighs about 60 tons. File:Willamette Meteorite AMNH.jpg, The
Willamette Meteorite The Willamette Meteorite, officially named WillametteMeteoritical Bulletin ...

Willamette Meteorite
on display at the American Museum of Natural History. It weighs about 14,500 kilograms (32,000 pounds). This is the largest meteorite ever found in the United States. File:Bendeg%C3%B3_meteorite,_front,_National_Museum,_Rio_de_Janeiro.jpg, The Bendegó meteorite, weighing 5,360 kilograms (11,600 pounds), was found in 1784 and brought in 1888 to its current location at
National Museum of Brazil The National Museum of Brazil ( pt, Museu Nacional) was Brazil's oldest scientific institution. It is located in the city of Rio de Janeiro, where it is installed in the Paço de São Cristóvão (Saint Christopher's Palace), which is inside ...
in Rio de Janeiro. It is the largest meteorite ever found in Brazil. File:Meteoric iron 635 kg - foto Marco Busdraghi.JPG, The Otumpa mass, meteoric iron weighing 635 kilograms (1,400 pounds), from the
Campo del Cielo Campo del Cielo refers to a group of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two ...

Campo del Cielo
, exhibited in the
Natural History Museum, London The Natural History Museum in London is a natural history museum Skeletons of '' Finnish_Museum_of_Natural_History_in_Helsinki.html" ;"title="Giganotosaurus">Shunosaurus'' (left) and ''Giganotosaurus'' (right) in the Natural History Museum ...

Natural History Museum, London
, found in 1783 in Chaco, Argentina. File:SikhoteAlinMeteorite.jpg, A individual meteorite from the 1947
Sikhote-Alin meteorite An iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and tae ...
shower (coarsest
octahedrite Octahedrites are the most common structural class of iron meteorite Iron meteorites, also known as siderite :''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type ...
, class IIAB). This specimen is about wide. File:ChingaMeteorite.jpg, A individual Chinga iron meteorite (
Ataxite Ataxites (from Greek meaning "without structure") are a structural class of iron meteorites with a high nickel content and show no Widmanstätten patterns upon etching. Characteristics Ataxites are composed mainly of meteoric iron, a native metal ...
, class IVB).Chinga meteorite
at Meteoritical Bulletin Database.
This specimen is about 9 centimeters wide. File:Meteorite_fragment_from_the_Cañon_Diablo_Meteorite.jpg, Meteorite fragment from the 90mm wide File:Gibeon Meteorite.jpg, The Gibeon Meteorite: Year found: 1836, Country: Namibia, individual weighing 3986 grams. This specimen is in the private collection of Howardite meteorites. File:Murnpeowie meteorite.jpg, Murnpeowie meteorite, with regmaglypts resembling thumbprints, discovered on Station,
South Australia South Australia (abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Austral ...

South Australia
in 1910.


See also

*
Glossary of meteoritics This is a glossary of terms used in meteoritics, the science of meteorites A meteorite is a solid piece of debris from an object, such as a comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object ...
* Hraschina meteorite *
Meteoritics Meteoritics is the science that deals with meteors, meteorites, and meteoroids. It is closely connected to cosmochemistry, mineralogy and geochemistry. A specialist who studies meteoritics is known as a ''meteoriticist''. Scientific research in ...


References


External links


Meteorite articles, including discussions of iron meteorites, in Planetary Science Research Discoveries


from Meteorites Australia {{DEFAULTSORT:Iron Meteorite