The crystal chemistry of clinopyroxene, orthopyroxene. and olivine from a crushed fragment of the H5 Zaoyang chondrite has been investigated by X-ray structure refinement and detailed microprobe analysis. The meteoritic pyroxenes have cell and polyhedral volumes which compare well with such data from terrestrial pyroxenes that typically crystallize at low-pressure, Fe2+ and Mg are rather disordered in M1 and M2 sites of clino- and orthopyroxenes; the closure temperatures of the exchange reaction are 600 and 512-degrees-C respectively, which is consistent with a reasonably fast cooling rate, estimated to be of the order of 1-degrees-C/day. The closure temperature for the intercrystalline Ca-Mg exchange reaction for clino- and orthopyroxenes is 900-degrees-C, as calculated from clino- and orthopyroxene intergrowth. The cooling rates obtained from Fe2+-Mg intracrystalline partitioning suggest a cooling of the order of degrees per day at temperatures of 600-500-degrees-C due to a strong loss of heat by irradiation.
Zaoyang Chondrite Cooling History From Fe2+-mg Intracrystalline Ordering In Pyroxenes / G. M. MOLIN;M. TRIBAUDINO;E. BRIZI. - In: MINERALOGICAL MAGAZINE. - ISSN 0026-461X. - 58(1994), pp. 143-150. [10.1180/minmag.1994.058.390.13]
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