The thermal decomposition and infrared spectrum of sabugalite were studied. The infrared spectrum was interpreted on the basis of site and factor symmetry analysis and correlated with the X-ray powder diffraction data. The dehydration of sabugalite is characterized by three endotherms. The anhydrous phase decomposes at 440-680 ~ On the basis of the infrared spectrum in Nujol, oxonium ions are postulated in the structure of sabugalite. The infrared spectrum in a KBr disk is probably influenced by the sample preparation mode. Sabugalite does not form a meta I hydrate. Its first new partly dehydrated phase is isostructural with metaautunite II. Sabugalite, HAI(

Infrared spectra of mineral possessing layer structure - liebigite, Ca2[UO2(CO3)3].(8-11) H2O, schroeckingerite, NaCa3[UO2(CO3)3]SO4F.10 H2O, voglite, Ca2Cu[UO2(CO3)4].6 H2O (?), and synthetic andersonite, Na2Ca[UO2(CO3)3].6 H2O - were measured and interpreted and compared with the published infrared spectra of ammonium, potassium, rubidium, and cesium dioxo-tricarbonatouranates(VI). From the analysis of the infrared spectra it follows - in accordance with the results of X-ray diffraction analysis - that in the dioxo-tricarbonatouranate(VI) complex anion, [UO2(CO3)3]4-, forming hexagonal bipyramid, three bidentately bonded carbonate groups are present in the equatorial plane (in liebigite and andersonite and apparently also in schroeckingerite and voglite). The coordinations of the SO42- and F- ions in schroeckingerite and of the fourth carbonate group (?) in voglite have not been elucidated.

NATURAL HISTORY MUSEUM, NATIONAL MUSEUM IN PRAGUE, 115 79 PRAGUE, t~. S. S. R. NUCLEAR RESEARCH INSTITUTE, 250 68 I~E2 NEAR PRAGUE, t~. S. S. R.The thermal decompositions of natural and synthetic andersonites were studied. Two partly overlapping dehydration steps and three partly overlapping decarbonation steps were observed. The second dehydration and the first decarbonation steps also partly overlap. During decarbonation, the gradual formation of sodium diuranate and monoclinic and hexagonal phases in the NazU2OT-CaUO4_ x system was proved. The results were correlated with measured infrared spectra using site and factor group analysis and X-ray structure analysis. The chemical formula inferred for natural andersonite, NazCa[UO2(CO3)3] ~_ 5.6H20, agrees with that proposed for its synthetic analogue.Andersonite has been found in several deposits and also synthetized by several authors. Infrared spectra of both natural and synthetic specimens and luminescence spectra of the mineral have been published.A thermal analysis of synthetic anders0nite has been described. According to the crystal structure of synthetic andersonite [1], only five water molecules in the formula were found in the final Fourier map. The possible statistical distribution of the remainder in a structure channel is presumed. On the basis of our preliminary conclusions [2, 3], the formula Na2Ca[UO2(CO3)3]. _ 5.6H20 was proposed for synthetic andersonite [1], In this paper, attention is especially paid to the content of molecular water in natural andersonite and for comparison in synthetic andersonite, using combined TG and DTA and IR spectroscopy. A complex contribution to the crystal chemistry of andersonite will be published elsewhere [4]. The paper forms part of the scientific reassessment of secondary uranium minerals from the collections of the National Museum in Prague.

Infrared spectra (4 000-400 cm-1) of solid samples in KBr microdisks were measured and interpreted for uranyl carbonate minerals, viz. rutherfordine and sharpite, and synthetic phases in the system UO3-CO2-H2O; the mineral schoepite was studied for a comparison as well. The ν3 fundamental belonging to the UO22+ antisymmetric stretching vibrations in rutherfordine, UO2CO3.x H2O (0.2 > x ≥ 0), lies in the same range as for the hydrothermal phases (985 to 978 cm-1), whereas in the case of sharpite, UO2CO3.H2O or (UO2)6(CO3)5(OH)2.7 H2O or M1-x2+.(H3O)2x(UO2)6(CO3)5(OH)4.(6-2x) H2O, this vibration appears in the range where it is displayed by phases formed at normal temperature and pressure (954-953 and 914-913 cm-1). The IR spectrum of schoepite, UO3.2H2O, is published for the first time.