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A combination of atomic force microscopy, scanning election microscopy, transmission electron microscopy, energy dispersive spectroscopy, electron diffraction, and X-ray diffraction were used to study reactions of 0.5-500 mg/L aqueous Pb with [Ca.sub.5][([PO.sub.4]).sub.3]OH, hydroxylapatite (HAP), at pH 6 and 22 [degrees] C. Following 2 h reaction time, concentrations of [Pb.sub.aq] ([[Pb.sub.aq]]) decreased from 500 mg/L to [is less than] 100 mg/L, and from 0.5- 100 mg/L to [is less than] 15 [micro]g/L. This loss of [Pb.sub.aq] from solution (i.e.. sorption) resulted partially from simultaneous dissolution of HAP and precipitation of [Pb.sub.5][([PO.sub.4]).sub.3]OH, hydroxypyromorphite (HPY), or another solid Pb phase. The initial saturation state with respect to HPY (defined as the ratio of the ion activity product to equilibrium solubility product) influenced strongly precipitation processes. At a high degree of saturation (initial [[Pb.sub.aq]] [is greater than] 100 mg/L), small nuclei or aggregates of poorly crystalline HPY precipitated homogeneously in solution. At intermediate saturation (initial [[Pb.sub.aq]] ~10-100 mg/L), large, euhedral needles of HPY precipitated homogeneously in solution. At a low degree of saturation (initial [[Pb.sub.aq]] [is less than] 10 mg/L), a needle-like Pb-containing phase grew heterogeneously on HAP These results agree well with concepts derived from nucleation and growth theories and demonstrate that initial saturation state influences strongly the sorption process.

Lead feldspar single crystals were annealed at T = 1050 and 1000 [degrees] C, starting from a disordered metastable configuration (Pb[F.sub.H] [Q.sub.od] = 0) and from an ordered configuration (Pb[F.sub.L], [Q.sub.od] = 0.89). Single-crystal data collection and refinement in space group I2/c show that the degree of Al-Si order increases to [Q.sub.od] = 0.42 after annealing the disordered Pb[F.sub.L] at 1050 [degrees] C and decreases to [Q.sub.od] = 0.70 after annealing the ordered Pb[F.sub.L] sample at 1000 [degrees] C. This suggests that the equilibrium [Q.sub.od] is between 0.70 and 0.42 for temperatures between 1000 and 1050 [degrees] C, where anorthite or strontium feldspar are almost completely ordered. A residual In the difference-Fourier map because of positional disorder was observed near the Pb site in all the refined crystals. The average y/[b.sub.Pb] coordinate changes with increasing AI-Si disorder, as Pb approaches the glide plane. A significant decrease in the intensity of b-type reflections was consequently observed. A spontaneous strain, with the main axis almost parallel to the a axis, is associated with Al-Si ordering. Pb polyhedral deformation related with [Q.sub.od] accounts for the observed strain. A calibrating equation, [Q.sub.od] = [(8.427(2) - a) / 0.048(3)][sup.1/2], has been calculated and applied to the unit-cell parameters obtained from subsequent thermal treatments and from Bruno and Facchinelli (1972) to define the evolution of the [Q.sub.od] vs. the treatment temperature. The thermal behavior of the [Q.sub.od] could then be bracketed, suggesting [T.sub.c] between 1150 and 1200 [degrees] C for the 12/c-C2/m phase transition induced by the AI-Si order-disorder process.

The electronic structures of mineral surfaces, investigated by electron tunneling spectroscopy (ETS) applied under favorable conditions rather than in vacuum on fresh, oxidized and aqueous-gold-treated lead sulphide (001) (Pbs (001)) surfaces, reveal the advantages and disadvantages of the method with reference to geochemical researches. The ETS spectra are almost similar to the ones predicted by the tunneling theory. The difference in the spectra of gold, fresh Pbs and oxidized Pbs are used in the identification and separation of the minerals.

The structure of quetzalcoatlite, [Zn.sub.6][Cu.sub.3][(Te[O.sub.3]).sub.2] [O.sub.6][(OH).sub.6]([Ag.sub.x][Pb.sub.y])[Cl.sub.x+2y], x + y [is less than or equal to] 2, Z = 1, was solved and refined using data collected at the Advanced Photon Source-GSE-CARS facility, using a 2 x 2 x 40 [[micro]m.sub.3] single crystal. The structure is trigonal, space group P[bar]31m, a = 10.145(1), c = 4.9925(9) [Angstrom], V = 445.0(1) [[Angstrom].sup.3], and was refined to R = 5.1 for 395 unique observed reflections. [Te.sup.6+][O.sub.6] octahedra and Jahn-Teller distorted [Cu.sup.2+][O.sub.4][(OH).sub.2] octahedra share edges to form layers parallel to (001), and Zn[O.sub.2][(OH).sub.2] tetrahedra share vertices to form six-member rings parallel to (001). Layers of octahedra and tetrahedra alternate along c, and form a new framework structure by vertex sharing. Channels through the framework parallel to c are occupied by Ag, Pb, and Cl ions. Electron microprobe analysis revealed Ag and Cl overlooked in the original microchemical analysis. Up to one-third of the Ag was substituted by Pb, and a Pb-rich analog may exist.