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Thermal behavior of davyne-group minerals
No full textThe thermal behaviour of microsommite (MC), davyne from Vesuvius (DV) and from Zabargad (DZ) was determined by X-ray single crystal data obtained employing a microfurnace connected to a four-circle diffractometer. Upon heating, the a parameter increased linearly, with similar thermal expansion rates for the three samples: the mean linear expansion coefficients, alpha(a), were 10.2(3). 10(-6), 13.4(7). 10(-6), 15.1(8). 10(-6) K-1 for MC, DV and DZ respectively.
At about 473 K both MC and DZ showed a discontinuity in the expansion of the c parameter. The mean linear expansion coefficient, alpha(c), changed abruptly from 16(4). 10(-6) K-1 for both minerals below the discontinuity to 2(1). 10(-6) and 3(1). 10(-6) K-1 for MC and DZ, respectively, above the discontinuity. In DV, however, the alpha(c) coefficient was constant between 293 und 827 K and equal to 1(2). 10(-6) K-1.
The substructure of MC was refined under room conditions (R=0.055 with 758 independent reflections) in space group P6(3) and at 943 K in space group P6(3) (R=0.062, with 750 independent reflections) and in space group P6(3)/m (R=0.065 with 394 independent reflections). By comparing the structural refinements the discontinuity could be related to the tilting of the tetrahedra connected along c: for T473 K was due to the small tetrahedral expansion. In DV, where the completely stretched structure was already realized under room conditions, no phase transition occured
Cr, Ni, and other Potentially Toxic Elements (PTEs) in serpentine soils from different ophiolite complexes (Liguria, Italy)
No full textMineralogical and chemical evolution of ochreous precipitates from the Libiola Fe-Cu-sulphides Mine (Eastern Liguria, Italy).
No full textLight elements in amphibole-phlogopite-bearing peridotites from the Ulten Zone (Eastern Alps, Italy): crystal chemistry and petrological application.
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