1. Thapelo Moloto 1, Gelu Costin 1*,, Razvan Andrei 2 1 Department of Geology, Rhodes University, Grahamstown, South Africa; 2 Department of Mineralogy, University of Bucharest * e-mail: t.moloto@ru.ac.za, g.costin@ru.ac.za, asean1@yahoo.com Mineral chemistry Mineral compositions identified are: olivine (Fo 76 ), orthopyroxene (En 73 ), Plagioclase (Ab 85-86 ), kamacite (Ni average ca. 5,98 wt.%), taenite (19.90 - 59,83 wt % Ni), troilite. The WDS scans showed the presence of minor apatite and chromite (Fig. 3), hematite and magnetite. The glass has an albite-rich composition. Figure 4 show the distribution of elements in and outside a chondrule (sample MA-05). Discussion Based on the petrography and mineralogy, the meteorites in this study have been classified as type L in the ordinary chondrite group. However, oxygen (O) isotope compositions and whole-rock chemistry will have to be investigated in order to ascertain this classification. The presence of apatite and chromite may suggest that the meteorites came from a reducing environment. The occurrence of chondrules and aluminosilicate glass suggests that the meteorites withstood high temperatures and thermal shock. This can be explained by either the canonical (shock wave) model and the differentiated parent body model proposed by Libourel and Krot (2007). The ideal model is the shock wave model which suggests that chondrules are a product of flash melting in a medium with a relatively high ambient pressure (P > 10 -3 bars) (Aleon, 2008). This model is supported by the presence of barred olivine textures associated with recrystallised olivine as well as by the undoulous extinction of the bigger porphiritic crystals. Petrography The four meteorites show barred olivine chondrules and porphyritic olivine-pyroxene chondrules with indistinct boundaries in some instances. The chondrules are mainly composed of olivine and orthopyroxene. Chondrule size ranges from 0.2 mm to approximately 4 mm. Sample MA- 06 shows a porphyritic olivine-pyroxene chondrule with olivine inclusions in orthopyroxene. Olivine crystals occur in different textures such as in barred olivine chondrules, porphyritic olivine-pyroxene chondrules, AOA’s, porphyro- clasts and olivine as recrystallised crystals. Metal and sulphides appear as opaque minerals in and around the boundaries of the chondrules. The matrix is mostly composed of olivine, sulphide iron, Fe-Ni metal and plagioclase. The mesostasis is mostly glass and silicate minerals. Analytical methods EPMA data was obtained at the Department of Geology, Rhodes University. A Jeol JXA 8230 Superprobe with 4 WD spectrometers was used at 15 kV, 20 nA, 1 micron beam spot, 10 sec counting time per peak and 5 sec per each background. ZAF correction matrix was used for quantification. WDS elemental maps were obtained under the same conditions using Stage Scan settings at 10 ms dwell time. PETROGRAPHIC AND MINERALOGIC STUDY OF CHONDRITE METEORITES Acknowledgements The use of Jeol JXA 8230 Superprobe, Rhodes University, instrument sponsored by NRF/NEP grant 40113 (UID 74464) is kindly acknowledged. References Aleon, J. 2008. Meteorites and the physico-chemical conditions in the early solar nebula. Physics and Astrophysics of Planetary Systems. 14, 1-42 Krot A. E., Hutcheon I. D., Brearley A. J., Pravdivtseva O. V., Pataev M. I., and Hohenberg C. M. 2006. Timescales and settings for alteration of chondritic meteorites. Meteorites and the Early Solar System II. Pp 525- 553 Libourel, G. and Krot A. N. 2007. Evidene for the presence of planetisimal material among the precursors of magnesian chondrules of nebular origin. Earth and Planetary Science Letters. 254. Pp 1-8 MacPherson, G.J., Simon, S.B, Davis, A.M.,Grossman, L., and Krot, A.N. 2006. Calcium-Aluminum-rich Inclusions: Major Unanswered Questions. Chondrites and the Protoplanetary Disk ASP Conference Series. 341. Pp 225-250 Weisberg, M.K., McCoy, T.J., and Krot, A.N. 2006. Systematics and Evaluation of Meteorite Classification. Meteorites and the Early Solar System II. Pp 19-52 Figure 3: WDS scans of chromite (A) and apatite (B) from sample MA-05 WDS Scans Figure 1. Photomicrographs of different textures of chondrules. A and B barred olivine chondrules in cross polarised light. C. Porphyritic olivine-pyroxene chondrules in plane polarised light. D. Olivine laths in a porphyritic chondrule (ppl) Figure 2. Backscattered electron images showing chondrules, fine grained matrix, Fe-Ni metal and Fe sulphides. A. Porphyritic chondrule with kamacite and taenite inclusions in a fine grained matrix. B. Barred olivine chondrule with interstitial glass. C. Porphyritic olivine-pyroxene chondrules surrounded by Fe-Ni metal and iron sulphide (troilite). D. Porphyritic chondrule with olivine laths. E. Chondrule with indiscernible boundary. F. Apatite (light grey) occuring within the matrix. Scale is 100 µm Introduction Meteorites enable us to understand the processes that occurred in the early planetary bodies of the solar system. They are classified into two groups: primitive (undifferentiated) meteorites and differentiated meteorites. Chondrites are primitive meteorites that did not undergo planetary differentiation. There are fifteen chondrite groups which consist of four components that occur in various proportions: chondrules, refractory inclusions (CAI), iron-nickel metal grains and/or metal-troilite aggregates, and a fine grained matrix (Krot et al., 2006). Chondrules are one of the oldest objects in meteorites derived from asteroids in the protoplanetary disk about 4.56 billion years ago. These chondrules later aggregated into chondrite bodies. CAIs are the oldest formed material rich in Ca, Al, and Ti. They are composed of highly refractory minerals such as, spinel, perovskite, anorthite, melilite and are valuable in that they preserve the history of the early solar system (MacPherson et al., 2005). Four chondrite meteorite samples (MA-05, MA-06, MU7-02, and SH2) from the Western Sahara region were analysed using optical microscopy and EPMA in order to asses their micro-textures and mineral chemistry and advocate for one of the existing models regarding the genesis of chondritic meteorites. Conclusions Four chondritic meteorites were analysed using optical microscopy and EPMA. Different chondrules with varying textures (mostly barred and porphyritic) are mainly composed of olivine and orthopyroxene All four meteorites are type L ordinary chondrites. Rare apatite, chromite and Ab-rich plagioclase in the matrix suggest a disperse distribution of CAI minerals. The present study supports the shockwave model under high temperature and pressure conditions. Further investigations on whole rock chemistry, Oxygen isotope compositions and equilibration temperatures are required. WDS element maps Figure 4. WDS element maps showing porphyritic olivine-pyroxene chondrules surrounded by troilite. Chromite is also present in the matrix. BSE Mapped area