Publication Date:
2011-04-01
Description:
We present electron-microprobe and single-crystal X-ray-diffraction data for a microlite-group mineral with a formula near NaCaTa2O6F from the Morro Redondo mine, Coronel Murta, Minas Gerais, Brazil. On the basis of these data, the formula is A(Na0.88Ca0.88Pb0.02{square}0.22){Sigma}2.00 B(Ta1.70Nb0.14Si0.12As0.04){Sigma}2.00 X[(O5.75(OH)0.25]{Sigma}6.00 Y(F0.73{square}0.27){Sigma}1.00. According to the new nomenclature for the pyrochlore-supergroup minerals, it is intermediate between fluornatromicrolite and "fluorcalciomicrolite". The crystal structure, Fd[IMG]f1.gif" ALT="Formula" BORDER="0"〉m, a = 10.4396(12) A, has been refined to an R1 value of 0.0258 (wR2 = 0.0715) for 107 reflections (MoK{alpha} radiation). There is a scarcity of crystal-chemical data for pyrochlore-supergroup minerals in the literature. A compilation of these data is presented here.
Print ISSN:
0008-4476
Topics:
Geosciences
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