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Structural variations induced by thermal treatment in lead feldspar (PbAl 2 Si 2 O 8 )

1998; Mineralogical Society of America; Volume: 83; Issue: 1-2 Linguagem: Inglês

10.2138/am-1998-1-216

1945-3027

M. Tribaudino, Piera Benna, E. Bruno,

Mineralogy and Gemology Studies

Other| February 01, 1998 Structural variations induced by thermal treatment in lead feldspar (PbAl 2 Si 2 O 8 ) Mario Tribaudino; Mario Tribaudino Dipartimento di Scienze Mineralogiche e Petrologiche, Turin, Italy Search for other works by this author on: GSW Google Scholar Piera Benna; Piera Benna Search for other works by this author on: GSW Google Scholar Emiliano Bruno Emiliano Bruno Search for other works by this author on: GSW Google Scholar American Mineralogist (1998) 83 (1-2): 159–166. https://doi.org/10.2138/am-1998-1-216 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Mario Tribaudino, Piera Benna, Emiliano Bruno; Structural variations induced by thermal treatment in lead feldspar (PbAl 2 Si 2 O 8 ). American Mineralogist 1998;; 83 (1-2): 159–166. doi: https://doi.org/10.2138/am-1998-1-216 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Lead feldspar single crystals were annealed at T = 1050 and 1000 degrees C, starting from a disordered metastable configuration (PbF H , Q od = 0) and from an ordered configuration (PbF L , Q od = 0.89). Single-crystal data collection and refinement in space group I2/c show that the degree of Al-Si order increases to Q od = 0.42 after annealing the disordered PbF H at 1050 degrees C and decreases to Q od = 0.70 after annealing the ordered PbF L sample at 1000 degrees C. This suggests that the equilibrium Q od is between 0.70 and 0.42 for temperatures between 1000 and 1050 degrees C, where anorthite or strontium feldspar are almost completely ordered. A residual in the difference-Fourier map because of positional disorder was observed near the Pb site in all the refined crystals. The average y/b Pb coordinate changes with increasing Al-Si disorder, as Pb approaches the glide plane. A significant decrease in the intensity of b-type reflections was consequently observed. A spontaneous strain, with the main axis almost parallel to the a axis, is associated with Al-Si ordering. Pb polyhedral deformation related with Q od accounts for the observed strain. A calibrating equation, Q od = [(8.427(2)-a) / 0.048(3)] (super 1/2) , has been calculated and applied to the unit-cell parameters obtained from subsequent thermal treatments and from Bruno and Facchinelli (1972) to define the evolution of the Q od vs. the treatment temperature. The thermal behavior of the Q od could then be bracketed, suggesting T c between 1150 and 1200 degrees C for the I2/c-C2/m phase transition induced by the Al-Si order-disorder process. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.