Bindi, L., Czank, M., Rothlisberger, F. and Bonazzi, P. (2001) Hardystonite from Franklin furnace: A natural modulated melilite. American Mineralogist, 86 (5-6). pp. 747-751.

Abstract

Natural hardystonite, (Ca3.85Na0.14Pb0.01)(Zn0.85Al0.07Mg0.03Mn0.043+Fe0.023+)Si2.00O7.00, from the type locality was reinvestigated with single crystal X-ray diffraction, microprobe analysis, and electron diffraction. The average structure, space group P (4) over bar2(1)m, a = 7.800(1) Angstrom. c = 5.000(1) Angstrom, was refined to R = 1.91% using 331 independent reflections. Hardystonite exhibits an incommensurate modulated structure. As in synthetic melilite-type compounds, modulation is two-dimensional, with tartan-like appearance: modulation vectors are q(1) = alpha (a(1)* + a(2)*) and q(2) = alpha(-a(1)* + a(2)*). A modulation wavelength lambda = 19.0(4) Angstrom was estimated by centering satellite reflections using a single-crystal diffractometer. TEM-EDX investigations proved the chemical composition of the sample to be slightly inhomogeneous, with stronger and sharper satellites in the regions where the composition approaches the Ca2ZnSi2O7 end-member. Geometrical parameters as well as anisotropic displacement ellipsoids of hardystonite are consistent with those of the other melilite-type compounds having a modulated character.

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