Mineralogy and petrology of Noventa Vicentina H4 chondrite.

This paper presents the results of a detailed investigation on mineral chemistry and pyroxene crystal chemistry of the Noventa Vicentina H4 chondrile, the fall of which was previously reported by Baldanza and Triscari (1978). The mineral chemistry of its silicate phases shows that olivine (Fo = 82,60%) and orthopyroxene (En =83.56%) are quite homogeneous. Opaque minerals are represented by kamacite, taenite and troilite. Opaque shock veins, undulatory extinction of olivine, and the very defective structure of the orthopyroxene classify the Noventa Vicentina chondrile in the S3 shocked class of Stoffler et al. (1991). The orthopyroxene shows very broad X-ray diffraction peaks, and only one crystal was found suitable for X-ray diffraction analysis. Structural refinement yielded a Rubs discrepancy factor of 7%. Notwithstanding the low precision ofthe data, the closure temperature of intracrystalline Fe2+ - Mg exchange of about 600 °C is consistent with that of other chondriles, indicating fast cooling due to considerable loss of heat by radiation.