Ataxite

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Ataxite
  Structural class  
ChingaMeteorite.jpg
The Chinga meteorite is an ataxite.
Group IVB or "Iron, ungrouped", occasionally IAB or others
CompositionMainly Meteoric iron, nickel (>18%), no Widmanstätten patterns
Meteoric iron phase diagram taenite kamacite ataxite.svg
A phase diagram showing the link between structural and chemical classification.
The Santiago Papasquiero meteorite, an ataxite found in 1958 in Durango, Mexico. It consists of a finely crystalline mix of kamacite & taenite, plus other minor minerals. Santiago Papasquiero is a strange ataxite that appears to be a completely metamorphosed and recrystallized octahedrite. Field of view ~2.5 cm across. This is a cut, polished, nitric acid-etched surface. Ataxite (Santiago Papasquiero Meteorite).jpg
The Santiago Papasquiero meteorite, an ataxite found in 1958 in Durango, Mexico. It consists of a finely crystalline mix of kamacite & taenite, plus other minor minerals. Santiago Papasquiero is a strange ataxite that appears to be a completely metamorphosed and recrystallized octahedrite. Field of view ~2.5 cm across. This is a cut, polished, nitric acid-etched surface.

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.

Contents

Characteristics

Ataxites are composed mainly of meteoric iron, a native metal found in meteorites that consists of the mineral taenite with minor amounts of plessite, troilite, and microscopic lamellae of kamacite. Ataxites are the most nickel-rich meteorites known; they usually contain over 18% nickel. [1] The high nickel content is the reason that they do not develop a Widmanstätten structure, because in this case kamacite can be exsolved from taenite only at such a low temperature (below about 600°C) where diffusion is already too slow. [2]

Classification

Most ataxites belong to the IVB group or are classified as "Iron, ungrouped" because they do not fit in any of the groups currently recognized by meteorite classification. Some ataxites belong to the IAB group and fall into the sHL (high-Au, low-Ni subgroup), sLH (low-Au, high-Ni subgroup), sHH (high-Au, high-Ni subgroup) and "ung" subgroup (does not fit any subgroup of IAB). Only a couple of ataxites have been classified into the IAB complex and the IIF, IVA, IIAB, IIIAB groups. [3]

Abundance

They are a rare class, with none of the about 50 observed iron meteorite falls being an ataxite, however, the largest meteorite ever, the Hoba meteorite (found 1920 in Namibia, weight 60 tons), belongs to this class. A Tibetan Buddhist statue, the Iron Man, was likely carved from an ataxite meteorite. It might even be made from a fragment of the Chinga meteorite. [4] [5] Other examples of ataxites are the Dronino meteorite and pieces of the Gebel Kamil.

See also

Related Research Articles

<span class="mw-page-title-main">Kamacite</span> Alloy of iron and nickel found in meteorites

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: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.

<span class="mw-page-title-main">Octahedrite</span> 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.

<span class="mw-page-title-main">Meteorite classification</span> Systems of grouping meteorites based on shared characteristics

In meteoritics, a meteorite classification system attempts to group similar meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especially mineralogical, petrological, chemical, and isotopic properties.

<span class="mw-page-title-main">Sikhote-Alin meteorite</span> 1947 meteorite impact in southeastern Russia

In southeastern Russia, an iron meteorite fell on the Sikhote-Alin Mountains in 1947. Large iron meteorite falls have been witnessed, and fragments have been recovered, but never before in recorded history has a fall of this magnitude occurred. An estimated 23 tonnes of fragments survived the fiery passage through the atmosphere and reached the Earth.

<span class="mw-page-title-main">Widmanstätten pattern</span> Crystal patterns found in some meteorites

Widmanstätten patterns, also known as Thomson structures, are figures of long phases of nickel–iron, found in the octahedrite shapes of iron meteorite crystals and some pallasites.

<span class="mw-page-title-main">Meteoric iron</span> Iron originating from a meteorite rather than from the Earth since formation

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 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.

<span class="mw-page-title-main">Hexahedrite</span>

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% and only rarely below 5.3%.

<span class="mw-page-title-main">Taenite</span> Alloy of iron and nickel found in meteorites

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 Fe,Ni and nickel proportions of 20% up to 65%.

<span class="mw-page-title-main">Iron meteorite</span> Meteorite composed of iron-nickel alloy called meteoric iron

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 meteorites originate from cores of planetesimals, with the exception of the IIE iron meteorite group.

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<span class="mw-page-title-main">Chinga meteorite</span> Meteorite found in Russia

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.

<span class="mw-page-title-main">Dronino meteorite</span> Iron meteorite found in Russia

The Dronino meteorite is a 40-kilogram (88 lb) iron meteorite that was found in the Ryazan Oblast of Russia in July 2000. It is classified as an ataxite.

<span class="mw-page-title-main">IAB meteorite</span> Group of iron meteorites

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.

<span class="mw-page-title-main">IVB meteorite</span> Type of iron meteorite

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<span class="mw-page-title-main">Nantan meteorite</span> Meteorite found in China

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<span class="mw-page-title-main">Nonmagmatic meteorite</span> Deprecated term formerly used in meteoritics

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.

<span class="mw-page-title-main">Mundrabilla (meteorite)</span> Meteorite found in Western Australia

The Mundrabilla meteorite is an iron meteorite found in 1911 in Australia, one of the largest meteorites found, with a total known weight of 22 tonnes and the main mass accounting for 12.4 tonnes.

<span class="mw-page-title-main">IIAB meteorites</span> Type of iron meteorite

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. Most 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.

<span class="mw-page-title-main">Aletai meteorite</span> Very large iron meteorite from Altay prefecture in Northern Xinjiang, China

The Aletai meteorite, previously also known as the Armanty meteorite or Xinjiang meteorite, is one of the largest known iron meteorites, classified as a coarse octahedrite in chemical group IIIE-an. In addition to many small fragments, at least five main fragments with a total mass over 74 tonnes have been recovered, the largest weighing about 28 tonnes.

References

  1. Vagn F. Buchwald, Handbook of Iron Meteorites. University of California Press, 1975
  2. F. Heide, F. Wlotzka, Meteorites, Messengers from Space, Springer-Verlag 1995, page 143
  3. "Meteoritical Bulletin Database". Meteoritical Society. Retrieved 18 December 2012.
  4. "Ancient Buddhist Statue Made of Meteorite, New Study Reveals". Science Daily. Retrieved 26 December 2012.
  5. BUCHNER, Elmar; SCHMIEDER, Martin; KURAT, Gero; BRANDSTÄTTER, Franz; KRAMAR, Utz; NTAFLOS, Theo; KRÖCHERT, Jörg (1 September 2012). "Buddha from space-An ancient object of art made of a Chinga iron meteorite fragment*". Meteoritics & Planetary Science. 47 (9): 1491–1501. Bibcode:2012M&PS...47.1491B. doi: 10.1111/j.1945-5100.2012.01409.x .