• journal_title：The Canadian Mineralogist
• Contributor：Michael Schindler ; Petre Mandaliev ; Frank C. Hawthorne ; Andrew Putnis
• Publisher：Mineralogical Association of Canada
• Date：2006-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.44.2.415
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：44
• issue：2
• firstpage：415
• section：Articles

Dissolution experiments on synthetic crystals of curite, Pb²⁺₃(H₂O)₂[(UO₂)₄O₄(OH)₃]₂, were done in HCl–H₂O solutions of pH 2.1 and 3.5, in doubly distilled water, in Sr²⁺–HCl–H₂O solutions of pH 2.7 and 5.5, and in Na₂CO₃ solutions of pH 10.5 for 24 h at 60°C. Examination by atomic force microscopy and optical microscopy reveals the formation of etch pits under near-neutral to strongly acidic solutions, and the formation of hillocks under strongly basic solutions. A new approach to the morphology of uranyl-oxide minerals is used to calculate the stability of edges and the morphology of etch pits and hillocks formed on the basal surface of curite. These calculations predict that the probability of occurrence of edges decreases in the sequence: [001], [011], [0kl], k < l, [0kl], k > l, [010]. Edges along the basal surface and of all observed etch-pits and hillocks are [001], [110] and [0kl], k < l, in agreement with the predictions. Etch pits formed at lower pH have lower relief and larger lateral extent than etch pits formed at higher pH, in accord with a decrease in stability of the edges with decreasing pH. Etch pits on the same basal surface have identical orientations, which violates the presence of a two-fold screw axis in the symmetry of the bulk structure. Cross sections of etch pits are characterized by steep edges and convex surfaces. A growth model of an etch pit formed in doubly distilled water explains this morphology by different rates of dissolution perpendicular to edges defined by right and left terminations of polyhedron chains. Differences in the symmetry of etch pits formed in Sr²⁺-bearing and non-Sr²⁺-bearing solutions are attributed to a nonstoichiometric detachment of polyhedra in the absence of Sr²⁺ in the vicinity of the etch pits. The formation of hillocks under basic conditions and an increase in the density of etch pits with decreasing pH suggest that the formation of etch pits depends more on the degree of protonation of the basal face and its edges than on the degree of undersaturation of the solution with respect to curite.