Iron Meteorite

Iron meteorites consist mostly of metallic iron alloyed with typically between ~5 to ~30 wt% nickel. The main metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn phases are kamaciteMore common than taenite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Kamacite, α-(Fe,Ni), contains 4-7.5 wt% Ni, and forms large body-centered cubic crystals that appear like broad bands or beam-like structures on the etched surface of a meteorite; its name is derived from the Greek word α-(Fe, Ni) and taeniteLess common than kamacite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Taenite, γ-(Fe,Ni), has 27-65 wt% Ni, and forms small crystals that appear as highly reflecting thin ribbons on the etched surface of a meteorite; the name derives from the Greek word for "ribbon." y-(Fe, Ni). Based on their group classification, they may also contain a small weight percentage of one or more of the following minerals:

1. GraphiteOpaque form of carbon (C) found in some iron and ordinary chondrites and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have, typically in the form of nodules: C
2. TroiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites., (iron sulfide): FeS
3. SchreibersiteNi-Fe phosphide mineral, (Fe,Ni)3P, yellowish in color and predominantly found in iron and stony-iron meteorites. Schreibersite can also be found in a variety of other meteorites including some acapulcoites, aubrites, enstatite chondrites and achondrites, lunars, ureilites, winonaites and a smattering of other meteorite types like CM, CO and CB. Schreibersite: (Fe,Ni)₃P
4. CoheniteFe-Ni-Co carbide, (Fe,Ni,Co)3C, that occurs as an accessory constituent in several iron meteorites, and coarse octahedrites with < 7 wt. % Ni.: (Fe,Ni,Co)₃C
5. Various silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the inclusions and other minerals.

Iron meteorites are classified into various chemical groups that fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If into 3 general types based on their texture driven by their nickel (Ni) content:

1. HexahedriteOne of the main types of iron meteorites composed almost entirely of kamacite and named for its cubic (hexahedral) cleavage of α-Fe-Ni crystals. Upon etching, hexahedrites do not display a Widmanstätten pattern, but do often exhibit fine, parallel lines called Neumann lines for their discoverer, Franz Neumann, who first studied: Ni < 6%
2. OctahedriteMost Common type of iron meteorite, composed mainly of taenite and kamacite and named for the octahedral (eight-sided) shape of the kamacite crystals. When sliced, polished and etched with an acid such as nitric acid, they display a characteristic Widmanstätten pattern. Spaces between larger kamacite and taenite plates are often: 6% < Ni < 16
3. Ni-Rich AtaxiteWork in Progress Relatively rare variety of iron meteorite (designated type D) made almost entirely of taenite, a solid solution of Fe and 27 to 65% Ni. The Greek name means "without structure" and refers to the lack of a visible Widmanstätten pattern (spindles of kamacite are visible only microscopically).: Ni > 16%

Iron meteorites containing >16% Ni nucleate kamacite at such low temperatures that large single crystals could not form over the 4.55 billion years of solar systemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. history; they lack a Widmanstätten patternCharacteristic cross-hatched pattern visible on the surface of octahedrites, pallasites and even large metal blebs in chondrite melts and mesosiderite nodules after polishing and etching with an acid solution like nital (nitric acid in solution with ethanol). The acid will preferentially etch the iron based on its nickel content - and are called Ni-rich ataxites (i.e. without structure). The Ni-poor ataxites are hexahedrites or octahedrites reheated in massive impacts, or artificially after they fell on Earth. (https://www.sciencedirect.com/book/9780124158450/encyclopedia-of-the-solar-system)

Iron meteoriteMeteorite composed mainly of iron (Fe) and nickel (Ni) in the form of two alloys, kamacite and taenite. Due to their metallic makeup and extraordinary weight, iron meteorites are easily distinguished from ordinary rocks. Also, because they rarely break up in the air and suffer much less from the effects with the highest bulk Ni content: Oktibbeha County (58.5 wt% to ~60 wt%)
Other notable high bulk Ni content iron meteorites: NWA 6259 (42.2 wt%), Santa Catharina (35.3%), Tishomingo (32.5 wt%)

Group IC is a cohenite-rich group

No iron meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and contains less than 5% Ni. ???? from Handbook