Stony-irons

Stony Irons. The stony iron meteorites are composed of substantial iron and siUcate components. The paHasites contain cm-sized ohvine crystals embedded ia a soHd FeNi metal matrix and have properties consistent with formation at the core mantle boundary of differentiated asteroids. The mesosiderites are composed of metal and siUcates that were fractured and remixed, presumably ia the near-surface regions of their parent bodies. 

Chondrites Achondrites Stony iron meteorites Iron meteorites... 

Meteorites General classification into stony, stony-iron and iron, each with an interesting mineralogy, notably the carbonaceous chondrites... 

Stony-iron Class of silicate-iron-based meteorites. 

Ganguly J. and Stimpfl M. (2000) Cation ordering in orthopyroxenes from two stony-iron meteorites implications for cooling rates and metal-silicate mixing. Geochim. Cosmo-chim. Acta 64, 1291-1297. 

Stony irons are nonchondritic meteorites that contain roughly equal proportions of silicate minerals and metal. Two types of stony irons - pallasites and mesosiderites - are distinguished. Pallasites consist of approximately equal amounts of metal and olivine (one small group contains pyroxene as well). Mesosiderates also have approximately equal proportions of metal and silicate, but the silicate fraction is basalt. 

Haack, H. and McCoy, T. J. (2004) Iron and stony-iron meteorites. In Treatise on Geochemistry, Volume 1 Meteorites, Comets, and Planets, ed. Davis, A.M. Oxford Elsevier, pp. 325-345. 

As already noted, spectral similarities between the various asteroid classes and specific types of meteorites provide a way to identify possible meteorite parent bodies. The Tholen and Barucci (1989) asteroid taxonomy has been interpreted as representing the types of meteorites shown in Table 11.1. Using the Bus et al. (2002) taxonomy, the C-complex asteroids are probably hydrated carbonaceous chondrites (e.g. Cl or CM). These carbonaceous chondrite asteroids probably accreted with ices and will be considered in Chapter 12. Some S-complex asteroids are ordinary chondrite parent bodies, but this superclass is very diverse and includes many other meteorite types as well. The X-complex includes objects with spectra that resemble enstatite chondrites and aubrites, and some irons and stony irons, although other X-complex asteroids are unlike known meteorite types. A few asteroid spectra are unique and provide more definitive connections, such as between 4 Vesta and... 

Anhydrous planetesimals, and especially the meteorites derived from them, provide crucial cosmochemical data. Spectroscopic studies of asteroids do not provide chemical analyses, but the spectral similarities of several asteroid classes to known meteorite types provide indirect evidence of their compositions. The few chemical analyses of asteroids by spacecraft are consistent with ordinary chondrite or primitive achondrite compositions. Laboratory analyses of anhydrous meteorites - chondrites, achondrites, irons, and stony irons - allow us to study important chemical fractionations in early solar system bodies. Fractionations among chondrites occur mostly in elements with higher volatility, reflecting the accretion of various components whose compositions were determined by high- and low-temperature processes such as condensation and evaporation. Fractionations among achondrites and irons are more complex and involve partitioning of elements between melts and crystals during differentiation. 

Meteorites are generally divided into three broad groups according to their chemistry and mineralogy that is, stones, stony irons, and irons (Chapman, 1999, 353 Dalrymple, 1991, 264). As the name implies, stony irons are meteorites with intermediate compositions between irons and stones (Dalrymple, 1991, 264). Stones mostly consist of carbonate minerals, magnesium- and iron-rich silicates, and/or other nonmetallic... 

Stony iron meteorite A meteorite consisting of a mixture of silicates and elemental iron-nickel. Its composition is intermediate between iron and stony meteorites. 

Hirata, T. (1997) Isotopic variations of germanium for iron and stony iron meteorites. Geochim. Cosmochim. Acta 61, 4439-4448. 

The stony-iron meteorites are intermediate between chondrites and irons. These very rare meteorites are equal mixtures of iron/nickel alloys and silicate minerals. Pallasites are striking examples of this type of meteorites, consisting of green olivine crystals in a matrix of metallic iron. Another type of stony-iron meteorite, called mesosiderites, contain pyroxene and plagioclase feldspars, minerals that are common on Earth. 

Figure 10.1 (a) a chondritic meteorite (b) a pallasite stony-iron meteorite (c) an iron meteorite (d) S-type asteroid 243 Ida (e) C-type asteroid 253 Mathilde. Credit NASA. 

Differentiated (planetary) Achondrites Angrites Aubrites Brachinites HED meteorites Eucrites Howardites Diogenites Ureilites Stony-irons Pallasites... 

The differentiated meteorites were derived from parent bodies that experienced large-scale partial melting, isotopic homogenization (ureilites are the only exception), and subsequent differentiation. Based on abundance of FeNi-metal, these meteorites are commonly divided into three types achondrites (metal-poor), stony irons, and irons each of the types contains several meteorite groups and ungrouped members. 

Pallasites are stony irons composed of roughly equal amounts of silicate (dominantly olivine), metal, and troilite (Figure 25). There are three separate pallasite types that are distinguished by differences in silicate mineralogy and composition (Table 6), metal, and oxygen isotopic... 

Haack H., Scott E. R. D., Love S. G., Brearley A. J., and McCoy T. J. (1996) Thermal histories of IVA stony-iron and iron meteorites evidence for asteroid fragmentation and reacrretion. Geochim. Cosmochim. Acta 60, 3103-3113. 

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