The crystal structures of natural celestine (Sr1.00)SO4, anglesite (Pb0.99Sr0.01)SO4, and barite (Ba0.99Sr0.01)SO4 have been refined in space group Pbnm utilizing rotating anode, Mo X-ray diffraction data from single crystals. Unit-cell parameters for celestine are a 6.8671(7), b 8.3545(8), and c 5.3458(6) Å, for anglesite, a 6.9549(9), b 8.472(1), and c 5.3973(8) Å, and for barite, a 7.154(1), b 8.879(2), and c 5.454(1) Å. Structural data are presented for these sulfates with greatly improved precision over previous studies owing to high peak-to-background intensity ratios and precise analytical absorption corrections. The final model R(F) values are 0.025, 0.041, and 0.019, for celestine, anglesite, and barite, respectively. The average bond-distance from divalent cation to the nearest twelve oxygen atoms is 2.827(1) Å in celestine, 2.864(5) Å in anglesite, and 2.951(2) Å in barite. The average sulfur-to-oxygen bond distance is 1.475(2) Å in celestine, 1.476(6) Å in anglesite, and 1.476(2) Å in barite. The sulfate tetrahedra in each structure show very similar distortions that are attributed to the bonding of the various oxygen atoms to the divalent cations, which is similar in each structure. Thus, the different metal cations do not seem to affect the size or shape of the sulfate tetrahedra. An analysis of the displacement parameters suggests that the SO4 groups behave as rigid molecular units, with an apparent shortening of the S-O bonds of 0.008-0.010 Å.
|Original language||English (US)|
|Number of pages||8|
|Publication status||Published - Aug 1998|
- Rigid-body motion
- X-ray-diffraction data
ASJC Scopus subject areas
- Geochemistry and Petrology