Stony-iron meteorite

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... 

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. 

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. 

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. 

Lovering J. F., Nichiporuk W., Chodos A., and Brown H. (1957) The distribution of gallium, germanium, cobalt, chromium, and copper in iron and stony-iron meteorites in relation to nickel content and structure. Geochim. Cosmochim. Acta 11, 263-278. 

The paUasites, coarse-grained stony-iron meteorites, also form three oxygen isotope groups the main group, the Eagle Station paUasites (three members), and the pyroxene paUasites (two members) (Clayton and Mayeda, 1996). 

PARENT BODIES OF IRON AND STONY-IRON METEORITES... 

Without iron and stony-iron meteorites, our chances of ever sampling the deep interior of a differentiated planetary object would be next to nil. Although we live on a planet with a very substantial core, we will never be able to sample it. Fortunately, asteroid collisions provide us with a rich sampling of the deep interiors of differentiated asteroids. 

Iron and stony-iron meteorites are fragments of a large number of asteroids that underwent significant geological processing in the early... 

Iron and stony-iron meteorites constitute —6% of meteorite falls (Grady, 2000). Despite their scarcity among falls, iron meteorites are our only samples of 75 of the 135 asteroids from which meteorites originate (Keil et ai, 1994 Scott, 1979 Meibom and Clark, 1999 see also Chapter 1.05), suggesting that both differentiated asteroids and the geologic processes that produced them were common. 

If the iron and stony-iron meteorites came from fully differentiated asteroids, how did these asteroids heat to the point of partial melting and how did the metal segregate from the silicates Unlike large planets, where potential energy release triggers core formation, small asteroids require an additional heat source. The heat source(s) for asteroidal melting produced a wide range of products, from unmetamorphosed chondrites to fully molten asteroids, as well as partially melted asteroids. Samples from these latter asteroids provide us with a rare opportunity to observe core formation—frozen in place. 

Table 1 Average compositions of meteorites from the major iron and stony-iron meteorite groups.

Parent Bodies of Iron and Stony-iron Meteorites... 

In this chapter, we have touched upon our current state of knowledge about iron and stony-iron meteorites, the processes that formed them and the places from which they originate. Our knowledge of all of these is far from complete. In this section, we briefly address the future of these fields. What questions remain unanswered Which are most pressing to understand the origin of iron meteorites What tools do we need to move forward ... 

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