IVB meteorite

IVB meteorites
	— Group —
	Tlacotepec is one of 14 known IVB specimens; in contrast to most IVBs it is an octahedrite instead of an ataxite
Type	Iron
Structural classification	Most are ataxites (without structure) but show microscopic Widmanstätten patterns
Class	Magmatic
Subgroups	None?;
Parent body	IVB
Composition	Meteoric iron (kamacite, taenite & tetrataenite); low in volatile elements, high in nickel & refractory elements
Total known specimens	14

Last updated April 09, 2019

IVB meteorites are a group of ataxite iron meteorites classified as achondrites.^[1] The IVB group has the most extreme chemical compositions of all iron meteorites, meaning that examples of the group are depleted in volatile elements and enriched in refractory elements compared to other iron meteorites.^[2]

Ataxites are a structural class of iron meteorites with a high nickel content and show no Widmanstätten patterns upon etching.

Iron meteorite meteorite composed of iron-nickel alloy called meteoric iron

Iron meteorites are meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Iron meteorites originate from cores of planetesimals.

In planetary science, volatiles are the group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, methane and sulfur dioxide. In astrogeology, these compounds, in their solid state, often comprise large proportions of the crusts of moons and dwarf planets.

Description

The IVB meteorites are composed of meteoric iron (kamacite, taenite and tetrataenite). The chemical composition is low in volatile elements and high in nickel and refractory elements. Although most IVB meteorites are ataxites ("without structure"), they do show microscopic Widmanstätten patterns. The lamellae are smaller than 20 µm wide and lie in a matrix of plessite.^[3] The Tlacotepec meteorite is an octahedrite, making a notable exception, as most IVBs are ataxites.^[4]

Meteoric iron, sometimes meteoritic iron, is a native metal found in meteorites and made from the elements iron and nickel mainly in the form of the mineral phases kamacite and taenite. Meteoric iron makes up the bulk of iron meteorites but is also found in other meteorites. Apart from minor amounts of telluric iron, meteoric iron is the only naturally occurring native metal of the element iron on the Earth's surface.

Kamacite is an alloy of iron and nickel, which is found on Earth only in meteorites. The proportion iron:nickel is between 90:10 and 95:5; small quantities of other elements, such as cobalt or carbon may also be present. The mineral has a metallic luster, is gray and has no clear cleavage although its crystal structure is isometric-hexoctahedral. Its density is about 8 g/cm³ and its hardness is 4 on the Mohs scale. It is also sometimes called balkeneisen.

Taenite (Fe,Ni) is a mineral found naturally on Earth mostly in iron meteorites. It is an alloy of iron and nickel, with nickel proportions of 20% up to 65%.

Classification

Iron meteorites were originally divided into four groups designated by Roman numerals (I, II, III, IV). When more chemical data became available some groups were split. Group IV was split into IVA and IVB meteorites.^[5] The chemical classification is based on diagrams that plot nickel content against different trace elements (e.g. gallium, germanium and iridium). The different iron meteorite groups appear as data point clusters.^[1]^[6]

Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion (passivation). Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.

Gallium is a chemical element with symbol Ga and atomic number 31. It is in group 13 of the periodic table, and thus has similarities to the other metals of the group, aluminium, indium, and thallium. Gallium does not occur as a free element in nature, but as gallium(III) compounds in trace amounts in zinc ores and in bauxite. Elemental gallium is a soft, silvery blue metal at standard temperature and pressure, a brittle solid at low temperatures, and a liquid at temperatures greater than 29.76 °C (85.57 °F).

Germanium Chemical element with atomic number 32

Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbours silicon and tin. Pure germanium is a semiconductor with an appearance similar to elemental silicon. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature.

Parent body

IVB meteorites formed the core of a parent body that was later destroyed, some of the fragments falling on Earth as meteorites.^[3] Modeling the IVB parent body has to take into account the extreme chemical composition, especially the depletion of volatile elements (gallium, germanium) and the enrichment in refractory elements (iridium) compared to other iron meteorites.^[2]

In planetary science, any material that has a relatively high equilibrium condensation temperature is called refractory. The opposite of refractory is volatile.

The history of the parent body has been reconstructed in detail. The IVB parent body will have formed from material that condensed at the highest temperatures while the solar nebula cooled off. The enrichment in refractory elements was caused by less than 10 % of the condensible material going into the parent body.^[2] Thermal models suggest that the IVB parent body formed 0.3 million years after the formation of the calcium-aluminium-rich inclusions, and at a distance from the sun of 0.9 Astronomical units.^[7]^[8]

The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that distance varies as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year. Originally conceived as the average of Earth's aphelion and perihelion, since 2012 it has been defined as exactly 149597870700 metres or about 150 million kilometres. The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec.

Differentiation of the planet body into a core and mantle was most likely driven by the heat produced by the decay of ²⁶Al and ⁶⁰Fe.^[9]^[10] The high nickel concentrations were caused by oxidizing physical conditions. The chemical variation of IVB specimens can be explained as different stages of the fractional crystallization of the convecting core of the parent body.^[3] The exact size of the parent body is still debated. Modelling of cooling rates suggest that it had a 140 ± 30 km radius with a 70 ± 15 km radius core. The fast cooling rates are explained by a grazing-shot collision of the parent body with a larger asteroid. This removed the mantle from the parent body, leaving the shattered iron core behind to rapidly cool.^[3]

In planetary science, planetary differentiation is the process of separating out different constituents of a planetary body as a consequence of their physical or chemical behavior, where the body develops into compositionally distinct layers; the denser materials of a planet sink to the center, while less dense materials rise to the surface, generally in a magma ocean. Such a process tends to create a core and mantle. Sometimes a chemically distinct crust forms on top of the mantle. The process of planetary differentiation has occurred on planets, dwarf planets, the asteroid 4 Vesta, and natural satellites.

The planetary core consists of the innermost layer(s) of a planet. Cores of specific planets may be entirely solid or entirely liquid, or may be a mixture of solid and liquid layers as is the case in the Earth. In the Solar System, core size can range from about 20% (Moon) to 85% of a planet's radius (Mercury).

A mantle is a layer inside a planetary body bounded below by a core and above by a crust. Mantles are made of rock or ices, and are generally the largest and most massive layer of the planetary body. Mantles are characteristic of planetary bodies that have undergone differentiation by density. All terrestrial planets, a number of asteroids, and some planetary moons have mantles.

Notable specimens

As of December 2012, 14 specimens of IVB meteorites are known.^[11] A notable specimen is the Hoba meteorite, the largest known intact meteorite. There has never been an observed fall of an IVB meteorite.^[11]

Related Research Articles

Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the entire Solar System, and has made important contributions to the understanding of a number of processes including mantle convection, the formation of planets and the origins of granite and basalt.

Octahedrite Structural class of iron meteorites

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.

The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planet, asteroid, Moon, or other current Solar System object, or one that existed some time in the past. However, with a few exceptions, this goal is beyond the reach of current science, mostly because there is inadequate information about the nature of most Solar System bodies to achieve such a classification. Instead, modern meteorite classification relies on placing specimens into "groups" in which all members share certain key physical, chemical, isotopic, and mineralogical properties consistent with a common origin on a single parent body, even if that body is unidentified. Several meteorite groups classified this way may come from a single, heterogeneous parent body or a single group may contain members that came from a variety of very similar but distinct parent bodies. As such information comes to light, the classification system will most likely evolve.

Chondrites are stony (non-metallic) meteorites that have not been modified due to melting or differentiation of the parent body. They are formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids. They are the most common type of meteorite that falls to Earth with estimates for the proportion of the total fall that they represent varying between 85.7% and 86.2%. Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life and the presence of water on Earth. One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, that normally constitute between 20% and 80% of a chondrite by volume.

Micrometeorite smallest extraterrestrial materials that make it to the surface of the Earth

A micrometeorite is essentially a micrometeoroid that has survived entry through Earth's atmosphere. The size of such a particle ranges from 50 µm to 2 mm. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. They are a subset of cosmic dust, which also includes the smaller interplanetary dust particles (IDPs).

Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion (4.6%) of meteorite falls.

Meteoritics is a science that deals with meteorites and other extraterrestrial materials that further our understanding of the origin and history of the Solar System. It is closely connected to cosmochemistry, mineralogy and geochemistry. A specialist who studies meteoritics is known as a meteoriticist.

An iron–nickel alloy or nickel–iron alloy, abbreviated FeNi or NiFe, is a group of alloys consisting primarily of the elements nickel (Ni) and iron (Fe). It is the main constituent of the "iron" planetary cores and iron meteorites. The acronym NiFe refers to various chemical reactions that involve an iron–nickel catalyst or component, or in geology, to the general composition of planetary cores.

Most atoms on Earth came from the interstellar dust and gas from which the Sun and Solar System formed. However, in the space science community, "extraterrestrial materials" generally refers to objects now on Earth that were solidified prior to arriving on Earth. In October 2011, scientists reported that one form of extraterrestrial material, cosmic dust, contains complex organic matter that could be created naturally, and rapidly, by stars. In February 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets.

The Chinga meteorite is an iron meteorite. It is structurally an ataxite with very rare kamacite lamella. The meteoric iron is a part of the lamella taenite. The total chemical composition is 82.8% iron, 16.6% nickel, and the rest mostly cobalt and phosphorus.

IAB meteorites are a group of iron meteorites according to their overall composition and a group of primitive achondrites because of silicate inclusions that show a strong affinity to winonaites and chondrites.

IIG meteorites are a group of iron meteorites. The group currently has six members. They are hexahedrites with large amounts of schreibersite. The meteoric iron is composed of kamacite.

Nonmagmatic meteorite is a deprecated term formerly used in meteoritics to describe iron meteorites that were originally thought to have not formed by igneous processes, to differentiate them from the magmatic meteorites, produced by the crystallization of a metal melt. The concept behind this was developed in the 1970s, but it was quickly realized that igneous processes actually play a vital role in the formation of the so-called "nonmagmatic" meteorites. Today, the terms are still sometimes used, but usage is discouraged because of the ambiguous meanings of the terms magmatic and nonmagmatic. The meteorites that were described to be nonmagmatic are now understood to be the product of partial melting and impact events and are grouped with the primitive achondrites and the achondrites.

This is a glossary of terms used in meteoritics, the science of meteorites.

IIAB meteorites are a group of iron meteorites. Their structural classification ranges from hexahedrites to octahedrites. IIABs have the lowest concentration of nickel of all iron meteorite groups. All iron meteorites are derived from the metallic planetary cores of their respective parent bodies, but in the case of the IIABs the metallic magma separated to form not only this meteorite group but also the IIG group.

References

1 2 M. K. Weisberg; T. J. McCoy, A. N. Krot (2006). "Systematics and Evaluation of Meteorite Classification" (PDF). In D. S. Lauretta; H. Y. McSween, Jr. Meteorites and the early solar system II. Tucson: University of Arizona Press. pp. 19–52. ISBN 978-0816525621 . Retrieved 15 December 2012.
1 2 3 Campbell, Andrew J.; Humayun, Munir (1 October 2005). "Compositions of group IVB iron meteorites and their parent melt". Geochimica et Cosmochimica Acta. 69 (19): 4733–4744. Bibcode:2005GeCoA..69.4733C. CiteSeerX 10.1.1.573.5611 . doi:10.1016/j.gca.2005.06.004.
1 2 3 4 Yang, Jijin; Goldstein, Joseph I.; Michael, Joseph R.; Kotula, Paul G.; Scott, Edward R.D. (31 July 2010). "Thermal history and origin of the IVB iron meteorites and their parent body". Geochimica et Cosmochimica Acta. 74 (15): 4493–4506. Bibcode:2010GeCoA..74.4493Y. doi:10.1016/j.gca.2010.04.011.
↑ "The Catalogue of Meteorites". nhm.ac.uk.
↑ McSween, Harry Y. (1999). Meteorites and their parent planets (Sec. ed.). Cambridge: Cambridge Univ. Press. ISBN 978-0521587518.
↑ Scott, Edward R. D.; Wasson, John T. (1 January 1975). "Classification and properties of iron meteorites". Reviews of Geophysics. 13 (4): 527. Bibcode:1975RvGSP..13..527S. doi:10.1029/RG013i004p00527.
↑ Bland, P. A.; F. J. Ciesla (2010). "The Impact of Nebular Evolution on Volatile Depletion Trends Observed in Differentiated Objects" (PDF). 41st Lunar and Planetary Science Conference. Retrieved 23 December 2012.
↑ Haghighipour, Nader; Scott, Edward R. D. (20 April 2012). "On the Effect of Giant Planets on the Scattering of Parent Bodies of Iron Meteorite from the Terrestrial Planet Region into the Asteroid Belt: A Concept Study". The Astrophysical Journal. 749 (2): 113. arXiv: 1202.2975 . Bibcode:2012ApJ...749..113H. doi:10.1088/0004-637X/749/2/113.
↑ Moskovitz, Nicholas; Eric Gaidos (2011). "Differentiation of Planetesimals and the Thermal Consequences of Melt Migration". Meteoritics and Planetary Science. 46 (6): 903–918. arXiv: 1101.4165 . doi:10.1111/j.1945-5100.2011.01201.x.
↑ Moskovitz, Nicholas A.; Walker, Richard J. (31 July 2011). "Size of the group IVA iron meteorite core: Constraints from the age and composition of Muonionalusta". Earth and Planetary Science Letters. 308 (3–4): 410–416. arXiv: 1106.2479 . Bibcode:2011E&PSL.308..410M. doi:10.1016/j.epsl.2011.06.010.
1 2 "Meteoritical Bulletin Database". Meteoritical Society. Retrieved 17 December 2012.

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[Weisberg_2006-1] 1 2 M. K. Weisberg; T. J. McCoy, A. N. Krot (2006). "Systematics and Evaluation of Meteorite Classification" (PDF). In D. S. Lauretta; H. Y. McSween, Jr. Meteorites and the early solar system II. Tucson: University of Arizona Press. pp. 19–52. ISBN 978-0816525621 . Retrieved 15 December 2012.

[Campbell_2005-2] 1 2 3 Campbell, Andrew J.; Humayun, Munir (1 October 2005). "Compositions of group IVB iron meteorites and their parent melt". Geochimica et Cosmochimica Acta. 69 (19): 4733–4744. Bibcode:2005GeCoA..69.4733C. CiteSeerX 10.1.1.573.5611 . doi:10.1016/j.gca.2005.06.004.

[Yang_2010-3] 1 2 3 4 Yang, Jijin; Goldstein, Joseph I.; Michael, Joseph R.; Kotula, Paul G.; Scott, Edward R.D. (31 July 2010). "Thermal history and origin of the IVB iron meteorites and their parent body". Geochimica et Cosmochimica Acta. 74 (15): 4493–4506. Bibcode:2010GeCoA..74.4493Y. doi:10.1016/j.gca.2010.04.011.

[The_Catalogue_of_Meteorites-4] "The Catalogue of Meteorites". nhm.ac.uk.

[McSween_1999-5] McSween, Harry Y. (1999). Meteorites and their parent planets (Sec. ed.). Cambridge: Cambridge Univ. Press. ISBN 978-0521587518.

[Scott_Wasson_1975-6] Scott, Edward R. D.; Wasson, John T. (1 January 1975). "Classification and properties of iron meteorites". Reviews of Geophysics. 13 (4): 527. Bibcode:1975RvGSP..13..527S. doi:10.1029/RG013i004p00527.

[Bland_2010-7] Bland, P. A.; F. J. Ciesla (2010). "The Impact of Nebular Evolution on Volatile Depletion Trends Observed in Differentiated Objects" (PDF). 41st Lunar and Planetary Science Conference. Retrieved 23 December 2012.

[Haghighipour_2012-8] Haghighipour, Nader; Scott, Edward R. D. (20 April 2012). "On the Effect of Giant Planets on the Scattering of Parent Bodies of Iron Meteorite from the Terrestrial Planet Region into the Asteroid Belt: A Concept Study". The Astrophysical Journal. 749 (2): 113. arXiv: 1202.2975 . Bibcode:2012ApJ...749..113H. doi:10.1088/0004-637X/749/2/113.

[Moskovitz_2011a-9] Moskovitz, Nicholas; Eric Gaidos (2011). "Differentiation of Planetesimals and the Thermal Consequences of Melt Migration". Meteoritics and Planetary Science. 46 (6): 903–918. arXiv: 1101.4165 . doi:10.1111/j.1945-5100.2011.01201.x.

[Moskovitz_2011b-10] Moskovitz, Nicholas A.; Walker, Richard J. (31 July 2011). "Size of the group IVA iron meteorite core: Constraints from the age and composition of Muonionalusta". Earth and Planetary Science Letters. 308 (3–4): 410–416. arXiv: 1106.2479 . Bibcode:2011E&PSL.308..410M. doi:10.1016/j.epsl.2011.06.010.

[Meteoritical_Bulletin_Database-11] 1 2 "Meteoritical Bulletin Database". Meteoritical Society. Retrieved 17 December 2012.