20996-31 - NWA Possible Achondrite Meteorite of Basaltic composition. In study. 103.6g

Petrographic description
Under petrographic microscope, the sample is maily formed by clinopyroxene phenocrysts (Fig. 2), and, in a minor proportion, by orthopyroxenes and highly altered feldspars in a fine-grained matrix. The rock is altered, with plagioclase phenocrysts transformed to albite and sericite (Fig. 3).
Clinopyroxene is augite, showing several cracks and deformation twins. The matrix is formed by very fine-grained plagioclase, K-feldspar and pyroxene microcrystals. Fe-Ti oxides are also in the matrix. The rock has medium-grained chlorite pseudomorphs, probably by the alteration of olivine grains. Few amygdules are found of 1 mm length (Figs. 4 and 5). Accessory apatite and titanite grains appear in the sample. Barite is placed in the alteration zones.
Chlorite is also developed in the matrix. The size of pyroxene phenocrystals is up to 3 mm, while the plagioclase has 1-2 mm. Pyroxene phenocrysts, feldspars and altered olivines represent, respectively, 15, 8 and 5% of sample. The sample has porphyritic texture.

The analyzed rock can be classified as basalt (Le Maître et al., 2005), moderately altered. Possible achondrite meteorite.

Mineralogy and textural properties of samples were studied on (30m-thick) polished thin sections using transmitted and reflected light microscopy at LPA (UA) and UGR.

Photomicrographs were performed by using:
o Petrographic microscope: ZEISS Assioskop (LPA-UA).
o Digital camera: Photometrics CoolSNAPcf
o Image capture Software: RS ImageTM v.1.8.6

Samples (polished thin-sections) also were studied under scanning electron microscope (Research Technical Services – UA). Minerals were located and identified using BSE mode on Hitachi S3000N SEM coupled with an X-ray detector Bruker XFlash 3001 for microanalysis (EDS) and mapping. Semi-quantitative EDS X-ray microanalysis was performed using EDS spot analysis with acquisition time 60s and maximum process time to achieve best resolution of peaks in spectra.

ANNEX II. REFERENCES
Le Maître, R.W. (Editor), Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., Bellieni, G., Dudek, A., Efremova, S., Keller, J., Lameyre, J., Sabine, P.A., Schmid, R., Sørensen, H. & Woolley, A.R. 2005. Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge University Press. Second Edition, revised, 236 p. Cambridge, UK.