Maresch, Walter V.; Miehe, Gerhard; Czank, Michael; Fuess, Hartmut; Schreyer, Werner
European Journal of Mineralogy Volume 3 Number 5 (1991), p. 899 - 904
published: Oct 2, 1991
manuscript accepted: May 29, 1991
manuscript received: May 13, 1991
ArtNo. ESP147050305005, Price: 29.00 €
Abstract Synthetic amphibole with a composition close to Na3 Mg5 [Si8O21/(OH)](OH)2 has been shown by Rietveld refinement of X-ray powder diffraction data to possess triclinic symmetry. Electron diffraction indicates the existence of a superstructure with a three-fold b lattice constant. X-ray powder diffraction at temperatures up to 340°C and differential scanning calorimetry show that the structure transforms reversibly through a complex 60°C transition zone to the common C2/m symmetry above approximately 160°C. We suggest that natural amphiboles, particularly those containing A-sites filled with Na+, should be examined closely for evidence of triclinic symmetry.