Crystal chemistry of synthetic pyromorphite-mimetite solid solutions

Marta Strycharczyk

Аннотация


Pyromorphite Pb5[PO4]3Cl, mimetite Pb5[AsO4]3Cl, and their solid solutions were synthesized from aqueous solutions. These minerals form a ternary system within apatite group of P63/m symmetry (hexagonal bipyramid). Natural pyromorphite usually contains several percent of As. Also, natural mimetite often contains PO4 substitutions. The objective of this study was determination of regularities in crystalline lattice parameters changes with anionic substitution of  and . The products were characterized using X-ray diffraction and scanning electron microscopy with microanalysis. The synthesis resulted in fine white precipitate. X-ray diffraction indicated crystalline character of the precipitate. Lattice parameters for end-members are in accordance with ICDD standards and equal for pyromorphite a = 10,009 Å and c = 7,338 Å and for mimetite a = 10,247 Å and c = 7,448 Å. Both lattice parameters increase proportionally to the increase of As substitution in pyromorphite in conformation with Vegard’s law.

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