The structural chemistry of kalipyrochlore, a "hydropyrochlore"
The structural chemistry of kalipyrochlore, a "hydropyrochlore"
The Canadian Mineralogist (June 1994) 32, Part 2: 415-420
The crystal structure of kalipyrochlore from the Lueshe carbonatite, Zaire (Fd3m, a 10.604 Aa), has been refined to R 1.62%. On the basis of XRD and EPMA data, the formula is ([H (sub 2) O] (sub 0.99) Sr (sub 0.05) Ca (sub 0.01) )(Nb (sub 1.80) Ti (sub 0.20) )- (O (sub 4.06) OH (sub 1.94) )([H (sub 2) O] (sub 0.86) K (sub 0.14) ), leading to the idealized formula Nb (sub 2) (O,OH) (sub 6<P6M><P255MI>p) H (sub 2) O, where p up to 1.75. Kalipyrochlore is extremely deficient in A cations, such that the dominant occupant of this site is H (sub 2) O; it has some OH at the site normally occupied only by O, and has >> 1 H (sub 2) O group pfu. The maximum H (sub 2) O content ranges from 1.00 pfu for ideal pyrochlores (two A cations pfu) to 1.75 H (sub 2) O pfu for defect pyrochlores (no A cations).
