Iron, IAB complex, sHH subgroup
28° 2′ S., 117° 58′ E. Two fragments constituting a single sickle-shaped mass having a combined weight of 16.5 kg were found in Western Australia, about 10 km east of Mount Magnet (Buchwald, 1975). The mass exhibits significant terrestrial weathering with no evidence of Melted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of 4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below. Click on Term to Read More or heat-affected zone. Mount Magnet is classified structurally as a plessitic Most 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 Click on Term to Read More (Opl) with More 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 needles of a few µm in size. This iron was initially classified as geochemically anomalous, but has since been included in the high-Au, high-Ni subgroup (sHH) of the IAB complex (Wasson and Kallemeyn, 2002).
Diagram credit: Worsham et al., Earth and Planetary Science Letters, vol. 467, p. 164 (2017)
‘Characterizing cosmochemical materials with genetic affinities to the Earth: Genetic and chronological diversity within the IAB Meteorite 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 Click on Term to Read More complex’
(https://doi.org/10.1016/j.epsl.2017.02.044) In a study of the IAB subgroups, employing precise Mo, W, and Os isotope data along with HSE and other literature data, Worsham et al. (2017) ascertained that the three sHH irons in the study (ALHA80104, Kofa, and Mount Magnet) have indistinguishable µ97Mo isotopic compositions with an average value of 24 (±3).
click on photo for a magnified view Diagram credit: Worsham et al., Earth and Planetary Science Letters, vol. 467, p. 160 (2017)
‘Characterizing cosmochemical materials with genetic affinities to the Earth: Genetic and chronological diversity within the IAB iron Work 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 complex’
(https://doi.org/10.1016/j.epsl.2017.02.044) In another analysis of siderophile elements in IAB irons, Worsham et al. (2016) revealed that Mount Magnet has a more fractionated HSE pattern compared to the other two sHH samples in their study, Kofa and ALHA80104, both of which have nearly identical HSE patterns and which are somewhat similar to two late-crystallized IIIB irons (see diagram below, where Grant is a dashed line and Chupaderos is a dotted line). Based on this analysis, they suggest that Mount Magnet may have formed from a distinct parental melt on a common The body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More.
Diagram credit: Worsham et al., GCA, vol. 188, p. 268 (2016)
‘Literally, "iron-loving" element that tends to be concentrated in Fe-Ni metal rather than in silicate; these are Fe, Co, Ni, Mo, Re, Au, and PGE. These elements are relatively common in undifferentiated meteorites, and, in differentiated asteroids and planets, are found in the metal-rich cores and, consequently, extremely rare on systematics of IAB complex iron meteorites: New insights into the formation of an enigmatic group’
(https://doi.org/10.1016/j.gca.2016.05.019) The interior structure of Mount Magnet is ataxitic, containing numerous ribbons of Ni-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 Click on Term to Read More, small grains and clusters of silicates, and monocrystalline grains of troilite—each of these inclusions are often rimmed by kamacite. Both small pockets and skeletal crystals of schreibersite are also present, the former usually surrounded by wide kamacite rims. To learn more about the relationships within the IAB complex and among other iron chemical groups, see the Appendix, Part III. The photo shown above is an 11.32 g partial slice of Mount Magnet.
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