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Laueite/stewartite epitaxy – a single-crystal diffraction study
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- Journal:
- Mineralogical Magazine / Volume 89 / Issue 2 / April 2025
- Published online by Cambridge University Press:
- 24 March 2025, pp. 234-241
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- Article
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Laueite/stewartite epitaxy was studied using single-crystal diffraction applied to a composite crystal from Hagendorf-Süd, Bavaria. The orientation relationships between the crystals of the two minerals was facilitated by using a non-conventional B
$\bar {1}$ space group setting for stewartite, giving unit cells with parallel axes and with as = 2al, bs = bl and cs = 2cl. Face indexing of the crystals of the two minerals confirmed the epitaxial relationship, with the {100} and {010} faces parallel. The plane of epitaxy is {010}. Refinement of laueite and stewartite datasets extracted from the composite-crystal data collection showed a significant decrease in the mean Mn-site bond distances in laueite, consistent with chemical analyses of the crystals that gave site compositions of Mn0.92Fe3+0.08 for stewartite and Mn0.66Mg0.17Fe3+0.17 for laueite. The epitaxial growth of laueite on {010} planes of stewartite appears to have been initiated by a change in solution chemistry. Possible paragenesis of the secondary phosphate minerals from primary triphylite is discussed.
