Original paper

Dorrite from Kopeisk, South Urals, Russia: crystal structure and cation ordering

Shchipalkina, Nadezhda V.; Zubkova, Natalia V.; Pekov, Igor V.; Koshlyakova, Natalia N.


The crystal structure of dorrite, a member of the rhönite group, from the burnt dump of a coal mine No. 45 in Kopeisk (South Urals, Russia) was solved by direct methods based on single-crystal X-ray diffraction data and refined to R = 0.0373 % [3937 reflections with I > 2σ (I)]. Dorrite is triclinic, space group P 1, V = 747.83(10) Å 3 . The empirical formula calculated on the basis of 20 O atoms pfu (Z = 2) from electron microprobe data is: Ca2.02 (Fe3+ 3.80Mg2.08Mn0.06Ti0.06)Σ6.00[(Al3.63Si2.05Fe 3+ 0.33)Σ6.01O20]. Based on refined numbers of electrons in the cation sites and on interatomic distances the simplified crystal-chemical formula (Z = 1) is: M8 Ca2 M9Ca2 M1(Fe3+ 0.7 Mg0.3)M2(Fe3+ 0.8Mg0.2)M3(Fe3+ 0.7Mg0.3)2 M4(Fe3+ 0.7Mg0.3)2 M5 Mg2 M6(Mg0.6Fe3+ 0.4)2 M7(Fe3+ 0.8Al0.2)2[ T1 (Si0.5Al0.5)2 T2(Si0.5 Al0.5)2 T3Al2 T4 Si2 T5 (Al0.6Fe 3+ 0.4)2 T6 (Al0.6 Fe 3+ 0.4)2]O40. The idealized formula is Ca4Mg4Fe 3+ 8[Al8Si4O40]. The crystal chemistry of rhönite-group minerals is discussed.


kopeiskdorritecation orderingrhönite groupcrystal structurepyrometamorphismsapphirine supergroup