The Maslyanino iron meteorite

--- Russia.

[311 kb] [295 kb]

Figures 1-2. A small slice of iron meteorite, displaying an etched face (left) and a polished face (right). This iron displays, on the etched face, the Widmanstatten pattern of alloy intergrowths in the nickel-iron matrix, plus inclusions of both tawny sulphide (troilite) and of silicate inclusions. The latter are rather unusual in iron meteorites, though they occur in a number of examples, such as Kodaikanal, Landes and Miles. Sample weight 11.92 grams. The slice is perfectly square-cut, 24x24x3 mm, the nominal specific gravity 6.90 (less than a typical iron meteorite, which is composed largely of Ni-Fe alloys). Sample from Blaine Reed, Denver show, September 2015.


"Rock of the Month #173, posted for November 2015" ---

A "silicated iron" meteorite

from Russia. The Maslyanino IAB iron meteorite is a fine octahedrite with silicate inclusions. A single mass of 26 kg was found by agronomist V.G. Okel' in a wheat field near Maslyanino village, Novosibirsk region, Siberia, Russia. Maslyanino (Wlotzka, 1995, p.793) assays 12.43% Ni, 70 ppm Ge, 29 ppm Ga and 1.0 ppm Ir. The main mass is in the Geological Museum of Novosibirsk (Wlotzka, 1995).

I am not aware of any published work on this interesting iron, which is strange, given that the TKW is 26 kg and material is widely available through meteorite dealers. A video showing the etching of a thin, polished slice of Maslyanino can be viewed on YouTube, courtesy of Polandmet.

A minority of iron meteorites contain silicate inclusions, in addition to the usual components such as Ni-Fe alloys, troilite, schreibersite and graphite. The IIE irons are especially prone to being "silicated irons" (Delaney, 2000). Some of the larger irons such as Campo del Cielo are largely inclusion-free, but occasional silicated samples indicate that the parent meteoroid was far from homogeneous. Twenty-seven examples are shown in the following table, with a capricious selection of references, weighted toward those with hand-specimen photographs.

Iron Meteorites with Silicate Inclusions, Classification of Topics Available on this Site
Class Names and select references
IAB Caddo County (Takeda et al., 2000), Campo del Cielo, Copiapo (Killgore et al., 2002), Kendall County (Grady et al., 2014), Landes (Mittlefehldt, 2005), Maslyanino, Ocotillo (Killgore et al., 2002), Pitts (McSween, 1999), Udei Station (Killgore et al., 2002; Haag, 2003), Zagora (Haag, 1997)
IIE Colomera, Elga, Miles (Brandstatter et al., 2013), Kodaikanal (Dodd, 1981), Sombrerete, Tarahumara, Weekeroo Station
IIICD Maltahohe, Carlton and Dayton (McCoy et al., 1993a,b)
IVA Bishop Canyon (Krot et al., 2005), Sao Joao Nepomuceno, Steinbach
UNGR Guin (Kurat et al., 2007), NWA 5549 (Heritage Auctions, 2013), NWA 6583, Tucson (Kurat et al., 2010)

[240 kb]

Figure 3. More slices of Maslyanino, showing nice etch. Note the generally smooth, subrounded outlines of the dark silicate inclusions. Blaine Reed collection, Denver show, September 2015.

The genesis of the many classes and smaller grouplets of meteorites has long been summarized as follows: 1) the chondrites are the consolidated detritus of the early solar nebula, formed by condensation from very high temperatures and modified by local remelting and cooling events, at variable distances from the young Sun, while 2) irons, stony-irons and the igneous achondrites formed in differentiated (i.e., melted and concentrically stratified) parent bodies, yielding an asteroid like a small version of the model for the Earth: iron core, silicate (achondrite) mantle, with some core-mantle mixing to form a thin boundary layer of metal and silicates (pallasites and mesosiderites). Variations on such models probably account for most meteorites, but the tremendous advances in meteorite research in the past 50 years have led to a more sophisticated view.

In the case of the iron meteorites, much attention was paid to chemical and textural classifications, beyond the earlier textural and structural divisions into octahedrites, hexahedrites and ataxites. John Wasson, Ed Scott and colleagues put much effort into analyses of select major, minor and trace elements that could, in samples of circa 1 gram of metal, provide insights into the evolution of the diversity of compositions. Earlier data on Ni, Ir, Ga and Ge were augmented by a range of elements of differing degrees of volatility and siderophile (iron-loving) affinity. These included Cu and Co, As and Sb, W and Au. Wasson et al. (1980) reclassified some Ni-poor IAB irons as IIICD. In contrast to the original concept of an iron-rich melt, sinking to the core of a differentiated body (the so-called magmatic irons), IAB and IIICD irons did not form by fractional crystallization of metallic magma but, perhaps, in the segregation of small pools of impact melt on the surface of an unequilibrated parent body (Scott and Wasson, 1975; Choi and Wasson, 1994). The IIICD irons contain inclusions with a mixture of silicates and phosphates, as well as more reduced minerals such as graphite and phosphides. The assemblages are not in equilibrium, and it is likely that liquid immiscibility played a role in the formation of these irons (McCoy et al., 1993a). The IIICD irons Maltahohe, Carlton and Dayton all contain silicate-bearing inclusions rich in troilite, graphite, schreibersite and phosphates (including uncommon phases such as brianite, panethite and chladniite (McCoy et al., 1993b).

The winonaites (such as Pontlyfni and Mount Morris (Wisconsin)) are achondrites that contain relict chondrules. Oxygen isotopes in winonaites match values in IAB and IIICD irons. Brecciation in an impact event is one obvious way in which chondrite clasts and achondrite melt could be mixed together (Benedix et al., 1998). The ungrouped achondrite Dhofar 500 is a breccia that may be related to winonaites and silicate-bearing irons (Lorenz et al., 2003).

In the case of the fine-grained ataxite irons, both IVA and IVB irons cooled fast, presumably in relatively small parent bodies, the low volatile contents perhaps the result of planetary outgassing. IVB is the group of magmatic irons with the highest Ni content (16-18 wt.%) and the lowest content of volatiles such as Ge (Rasmussen et al., 1984). The IVA irons may contain silicate inclusions. Some of these are mixtures of pyroxenes and tridymite, possible cumulates. Coarse textures and mutual intergrowths of pyroxenes and tridymite are consistent with slow crystallization in the core of the IVA parent body. Some may have formed at high temperatures near the core-mantle boundary of a differentiated parent body (Ulff-Moller et al., 1995).

The IIE irons are non-magmatic irons which, unlike magmatic irons, not only contain the inclusions but also fail to show geochemical trends indicative of fractional crystallization of a slow-cooled metallic melt. Mont Dieu, the largest-known IIE iron, contains cm-size silicate inclusions with relict chondrules, in which oxygen isotopes are consistent with origin as an H-chondrite. The metal and silicate inclusions may have formed by impact on the H-chondrite parent body early in solar system history. According to the nature of their silicate assemblages, IIE irons are classified as primitive (1) to differentiated (5), thus (1) Netschaevo and Mont Dieu, with preserved, relict chondrules, (2) Techado, (3) Watson, (4) Miles and Weekeroo Station and (5) Elga, Colomera and Kodaikanal. A separate relation by age of formation recognizes old, circa 4500 Ma examples (Weekeroo Station, Miles, Colomera and Techado) and a younger, 3600 Ma event (Netschaevo, Kodaikanal and Watson, see Van Roosbroek et al., 2015).

References

Benedix,GK, McCoy,TJ, Keil,K, Bogard,DD and Garrison,DH (1998) A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism. Geochimica et Cosmochimica Acta 62, 2535-2553.

Brandstatter,F, Ferriere,L and Koeberl,C (2013) Meteoriten - Meteorites: Zeitzeugen der Entstehung des Sonnensystems / Witnesses of the Origin of the Solar System. Verlag des Naturhistorisches Museum, Vienna, 270pp. (in Engl. and in Ger.).

Choi,B-G and Wasson,JT (1994) Formation of IAB and IIICD iron meteorites. Lunar and Planetary Science 25, 255-256.

Delaney,JS (2000) IIEs or not IIEs: reduction is the question. Meteoritics & Planetary Science 35, A48.

Dodd,RT (1981) Meteorites: a Petrologic-Chemical Synthesis. Cambridge University Press, 368pp.

Grady,MM, Pratesi,G and Moggi-Cecchi,V (2014) Atlas of Meteorites. Cambridge University Press, 373pp.

Haag,RA (1997) The Robert A. Haag Collection Field Guide of Meteorites. 12th Anniversary Edition, Tucson, AZ, 60pp.

Haag,RA (2003) The Robert Haag Collection of Meteorites. Robert Haag Meteorites, Tucson, AZ, private collection edition, 126pp.

Heritage Auctions (2013) The Hoppel Collection of Fine Minerals, Auction 1 (session 1): and session 2, Natural History. Heritage Auctions, Dallas, TX, 2-part auction catalogue, available as a 366pp., 38.1 MB pdf file: Hoppel (228pp.) and Natural History (138pp.) (02 June).

Killgore,K, Killgore,M and Killgore,E (2002) Southwest Meteorite Collection, a Pictorial Catalog. Southwest Meteorite Press, 201pp.

Krot,AN, Keil,K, Goodrich,CA, Scott,ERD and Weisberg,MK (2005) Classification of meteorites. In `Meteorites, Comets, and Planets' (Davis,AM editor). Treatise on Geochemistry volume 1 (Holland,HD and Turekian,KK editors), Elsevier- Pergamon, Oxford, 737pp., 83-128.

Kurat,G, Zinner,E and Varela,ME (2007) Trace element studies of silicate-rich inclusions in the Guin (UNGR) and Kodaikanal (IIE) iron meteorites. Meteoritics & Planetary Science 42, 1441-1463.

Kurat,G, Varela,ME, Zinner,E and Brandstatter,F (2010) The Tucson ungrouped iron meteorite and its relationship to chondrites. Meteoritics & Planetary Science 45, 1982-2006.

Lorenz,CA, Ivanova,MA, Nazarov,MA, Mayeda,TK and Clayton,RN (2003) A new primitive ungrouped achondrite, Dhofar 500: links to winonaites and silicate inclusions from IAB-IIICD irons. Meteoritics & Planetary Science 38, A30.

McCoy,TJ, Keil,K, Scott,ERD and Haack,H (1993a) Genesis of the IIICD iron meteorites: evidence from silicate-bearing inclusions. Meteoritics 28, 552-560.

McCoy,TJ, Steele,IM, Keil,K, Leonard,BF and Endress,M (1993b) Chladniite: a new mineral honoring the father of meteoritics. Meteoritics 28, 394.

McSween,HY (1999) Meteorites and their Parent Bodies. Cambridge University Press, 2nd edition, 310pp.

Mittlefehldt,DW (2005) Achondrites. In `Meteorites, Comets, and Planets' (Davis,AM editor). Treatise on Geochemistry volume 1 (Holland,HD and Turekian,KK editors), Elsevier- Pergamon, Oxford, 737pp., 291-324.

Olsen,EJ and Schwade,J (1998) The silicate inclusions of the Ocotillo IAB iron meteorite. Meteoritics & Planetary Science 33, 153-155 (1998).

Rasmussen,KL, Malvin,DJ, Buchwald,VF and Wasson,JT (1984) Compositional trends and cooling rates of group IVB iron meteorites. Geochimica et Cosmochimica Acta 48, 805-813.

Scott,ERD and Wasson,JT (1975) Classification and properties of iron meteorites. Rev.Geophys.Space Phys. 13 no.4, 527-546.

Takeda,H, Bogard,DD, Mittlefehldt,DW and Garrison,DH (2000) Mineralogy, petrology, chemistry, and 39Ar- 40Ar and exposure ages of the Caddo County IAB iron: evidence for early partial melt segregation of a gabbro area rich in plagioclase-diopside. Geochimica et Cosmochimica Acta 64, 1311-1327.

Ulff-Moller,F, Rasmussen,KL, Prinz,M, Palme,H, Spettel,B and Kallemeyn,GW (1995) Magmatic activity on the IVA parent body: evidence from silicate-bearing iron meteorites. Geochimica et Cosmochimica Acta 59, 4713-4728.

Van Roosbroek,N, Debaille,V, Pittarello,L, Goderis,S, Humayun,M, Hecht,L, Jourdan,F, Spicuzza,MJ, Vanhaecke,V and Claeys,P (2015) The formation of IIE iron meteorites investigated by the chondrule-bearing Mont Dieu meteorite. Meteoritics & Planetary Science 50, 1173-1196.

Wasson,JT, Willis,J, Wai,CM and Kracher,A (1980) Origin of iron meteorite groups IAB and IIICD. Z.Naturforsch. 35a, 781-795.

Wlotzka,F (1995) The Meteoritical Bulletin, No.78, 1995 November. Meteoritics 30, 792-796.

Graham Wilson, 16,17,26 October 2015, 01,02,08,10 November 2015, update 14 January 2016

Visit the Turnstone Meteorite Index

or the broader "Rock of the Month" Archives!