Ataxite

Work in Progress

Relatively rare variety of iron meteoriteIron meteorites consist mostly of metallic iron alloyed with typically between ~5 to ~30 wt% nickel. The main metal phases are kamacite α-(Fe, Ni) and taenite y-(Fe, Ni). Based on their group classification, they may also contain a small weight percentage of one or more of the following minerals: • Click on Term to Read More (designated type D) made almost entirely of 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." Click on Term to Read More, a solid solutionCompositional variation resulting from the substitution of one ion or ionic compound for another ion or ionic compound in an isostructural material. This results in a mineral structure with specific atomic sites occupied by two or more ions or ionic groups in variable proportions. Solid solutions can be complete (with of Fe and 27 to 65% Ni. The Greek name means “without structure” and refers to the lack of a visible 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 - Click on Term to Read More (spindles of 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 Click on Term to Read More are visible only microscopically).

“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 pattern 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/topics/earth-and-planetary-sciences/taenite

Need more info as “Classification and Properties of Iron Meteorites” (https://www.higp.hawaii.edu/~escott/Scott%20n%20Wasson%201976%20rev%20irons.pdf) says Fine plessiteA fine-grained intergrowth of kamacite and taenite that fills in the wedges between wide kamacite and taenite bands in octahedrites. The name derives from the Greek word for "filling." Click on Term to Read More, generally some isolated kamacite platelets

Chinga ataxite 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 Click on Term to Read More (lacks Widmanstätten beacuseof its Ni content). Image source: http://www.arizonaskiesmeteorites.com/Widmanstatten/.