Esseneite from xenoliths in dacite lavas. Crystal structure and genesis

Yakubovich O. V., Zayakina N. V., Oleinikov O. B., Kostin A. V.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2017. V. 146. N 5. P. 105-115

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Language: Russian

Abstract

Esseneite from xenoliths of ultrabasic rocks in dacite lavas of the Ten’-01 paleovolcano at the Lena-Vilyui watershed (East Yakutia) was studied. Empirical formula of the mineral has been obtained using electron microprobe analysis: Ca_0.99Mg_0.32Ti_0.05Al_0.71Si_1.34O₆. Its crystal structure was refined on the basis of the single-crystal X-ray diffraction data, R 0.0152). The resulting crystal chemical formula is ^CaCa^M(Mg_0.33Ti_0.05Al_0.14)^T(Si_1.28Al_0.68)O₆. The monoclinic unit-cell parameters are: а = 9.7610(12), b = 9.8223(8), с = 5.3360(5) A, β = 105.92(1)°, V = 441.89(8) ų, Z =4, space group С2/с. The distribution of atoms over positions in the crystal structures of Ca-Fe-Al-clinopyroxenes and coordination polyhedra distortion reflect the conditions for the mineral genesis. Formation of the Yakutian esseneite took place in a highly oxidizing environment under a pressure of about 2 kbar and a temperature range of 1200—950 °C.

Key words: esseneite, crystal structure, Ten’-01 paleovolcano, Yakutia.