Meteorites magnesium

The largest class of meteorite finds is stony meteorites, made principally of stone. The general stony classification is divided into three subclasses called chondrites, carbonaceous chondrites and achondrites, and it is at this level of distinction at which we will stop. Before looking at their mineral and isotopic structure in more detail, it is useful to hold the composition of the Earth s crust in mind here for comparison. The Earth s crust is 49 per cent oxygen, 26 per cent silicon, 7.5 per cent aluminium, 4.7 per cent iron, 3.4 per cent calcium, 2.6 per cent sodium, 2.4 per cent potassium and 1.9 per cent magnesium, which must have formed from the common origin of the solar system. 

Another isotopic anomaly, discovered in Allende inclusions, concerns magnesium, for which an intrinsically low abundance in these samples makes its isotope ratios sensitive to small effects. Certain of the inclusions show a correlation between 26Mg and 27 Al, indicating an origin of excess 26Mg from radioactive decay of 26 A1 (mean life 1 Myr), the existence of which had previously been postulated as a heat source for meteorite parent bodies (Fig. 3.32). Other short-lived activites that seem to have been alive in the early Solar System are 10Be (mean life 2.2 Myr) from a correlation of 10B with 9Be, and 41Ca (mean life 0.15 Myr) from a correlation of... 

Molin G.M., Saxena S.K., and Brizi E. (1991) Iron-magnesium order-disorder in an orthopyroxene crystal from the Johnstown meteorite. EarthPlanet. Sci. Lett. 105, 260-265. 

Among the elements that make up rocks and minerals, silicon, magnesium, and iron are of almost equal abundance followed by sulfur, aluminum, calcium, sodium, nickel, and chromium. Two of the most common minerals in meteorites and in the terrestrial planets are olivine ((Mg,Fe)2Si04) and pyroxene ((Mg,Fe,Ca)Si03). The composition obtained by averaging these two minerals is very similar to the bulk solar system composition, so it is really no surprise that they are so abundant. 

Nagashima, K., Krot, A.N. and Chaussidon, M. (2007) Aluminum-magnesium isotope systematics of chondrules from CR chondrites (abstr.). Meteoritics and Planetary Science, 42, Supplement, All5. 

Plot of nickel versus magnesium in Martian rocks and meteorites. GRS-estimated Mg content is also shown. After McSween et al. (2009). 

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... 

The results obtained by averaging the analyses of 318 iron and 125 stone meteorites, 443 in all, show that the first seven elements m order of abundance are iron, nickel, silicon, magnesium, sulphur, and calcium ... 

Gallino R., Raiteri C. M., Busso M., and Matteucci F. (1994) The puzzle of silicon, titanium, and magnesium anomalies in meteoritic silicon carbide grains. Astrophys. J. 430, 858-869. 

New phosphoms and titanium XRF data for Cl chondrites were reported by Wolf and Palme (2001). The change in phosphorus is significant. The new Cl abundance is 926 ppm, which is much lower than the values in the older compilations, 1,105 ppm in Palme and Beer (1993) and 1,200 ppm in Anders and Grevesse (1989), respectively. The new phosphorus contents are considered to be more reliable. The changes in titanium are small. Wolf and Palme (2001) also reported major element concentrations of Cl meteorites and other carbonaceous chondrites. Their magnesium and silicon contents were almost identical to those given by Palme and Beer (1993) 10.69% versus 10.68% (for silicon) in Palme and Beer (1993) and 9.60% versus 9.61 % (for magnesium) in Palme and Beer (1993). The aluminum, calcium, and iron concentrations... 

Mayeda K., Clayton R. N., Krung D. A., and Davis M. (1988) Oxygen, silicon and magnesium isotopes in Ningqiang chondrules. Meteoritics 23, 288. 

Mean ratio of refractory lithophiles relative to magnesium, normalized to Cl chondrites. Includes chondrule fragments and silicates inferred to be fragments of chondrites, for all matrix in CH and CBb chondrites (Greshake et at, 2002). Fall frequencies based on 918 falls of differentiated meteorites and classified chondrites (Grady, 2000). 

Figure 22 Combined elemental map in magnesium (red), calcium (green), and A1 K (blue) X-rays ((a), (b)) and backscattered electron images ((b), (d)) of two barred or skeletal olivine chondrules, and a combined X-ray map (e) and NiKa scanning map (f) of a zoned Fe,Ni metal grain with an enclosed cryptocrystalline chondrule (CC) in the CBb chondrite HaH 237 (Krot et al, 2002a). The chondrules, which contain forsteritic olivine (ol), low-calcium pyroxene (px), high-calcium pyroxene (cpx) and mesostasis (mes), lack rims and relict grains and clearly formed in a dust-free environment from total melts (reproduced by permission of University of Arizona on behalf of The Meteoritical...

Folco L., Mellini M., and Pillinger C. T. (1997) Equilibrated ordinary chondrites constraints for thermal history from iron-magnesium ordering in orthopyroxene. Meteorit. Planet. Sci. 32, 567-575. 

Imai H. and Yurimoto H. (2000) Oxygen and magnesium isotopic distributions in a Type C CAI from the Allende meteorite. In Lunar Planet. Sci. XXXI, 1510. The Lunar and Planetary Institute, Houston (CD-ROM). 

Krot A. N., Sahijpal S., McKeegan K. D., Weber D., Greshake A., Ulyanov A. A., Hutcheon I. D., and Keil K. (1999) Mineralogy, aluminum-magnesium and oxygen isotope studies of the relict calcium-aluminum-rich inclusions in chondrules. Meteorit. Planet. Sci. 34, A68-A69. 

Misawa K. and Fujita T. (2000) Magnesium isotopic fractionations in barred olivine chondrules from the Allende meteorite. Meteorit. Planet. Sci. 35, 85-94. 

Srinivasan G., Krot A. N., and Ulyanov A. A. (2000b) Aluminum-magnesium systematics in anorthite-rich chon-dmles and calcium-aluminum-rich inclusions from the reduced CV chondrite Efremovka. Meteorit Planet Sci. 35, A151-A152. 

Hashimoto A. and Grossman L. (1987) Alteration of Al-rich inclusions inside amoeboid olivine aggregates in the AUende meteorite. Geochim. Cosmochim. Acta 51, 1685-1704. Hinton R. W. and Bischoff A. (1984) Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites. Nature 308, 169-172. 

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