CRYSTAL CHEMICAL STUDIES OF SOME URANYL OXIDE HYDRATES

Abstract

Mineralogical and crystal-chemical studies were made of the closely related uranyl oxide hydrates becquerelite, billietite, fourmarierite, masuyite, schoepite, and vandendriesscheite. An essertial feature of the work is the use of x-ray precession techniques with carefully selected single crystals to determine accurately the crystallographic constants, the symmetry, and the structural relations of these minerals. Indices of refraction and optical orientation were determined on crystals both identified and oriented by the x-ray precession method. Similarly identified crystals were used to obtain the indexed powder pattern data listed. The results obtained on the physical properties, the x-ray crysthllography, the x-ray powder data, and the optical properties are listed and compared with the work of other investigators in the 23 tables of the paper. Crystals of schoepite and of vandendriesscheite that are apparently single actually consist of several crystallographically distinct phases in parallel intergrowth. The spontaneous alteration from one phase to another that occurs in these crystals results from loss of water of hydration. All six of the minerals studied yield strikingly similar pseudohexagonal diffraction patterns. A reasonable crystal structure based on these patterns consists of UO/sub 2/(OH)/ sub 2/ layers (similar to those proved by Zachariasen to exist in UO/sub 2/F/sub 2/) parallelmore » to the perfect cleavage (OOl), with the water of hydration and any cations present in interlayer positions. (auth)« less