High temperature solvent growth of anorthite on the join CaAl2Si2O8-SiO2 |
| |
| Authors: | Jun Ito |
| |
| Institution: | (1) The James Franck Institute, The University of Chicago, 60637 Chicago, Illinois, USA |
| |
| Abstract: | Stoichiometric anorthite, CaAl2Si2O8, P¯1, with sharp a, b, c, and d diffractions was grown, using a CaV2O6 solvent, by cooling at 2 ° C per hour from 1450 to 750 ° C in air. Euhedral crystals up to 5 × 3× 0.5 mm, with prominent {010} and well-developed {110} and {001}, were obtained by spontaneous nucleation. Nonstoichiometric anorthite with excess SiO2 (CaAl2Si2O8+Si2Si2O8) was grown on the join CaAl2Si2O8-SiO2. Chemical analysis of the synthetic anorthite, having the highest SiO2 content, with maximum vacancies on M-site gave □0.110 Na0.006Ca0.884Al1.80Si2.20O8, and X-ray diffraction showed a trend from stoichiometric P¯1 through diffuse P¯1 to body-centered I¯1 probably reflecting increasing disorder caused by a higher Si/Al ratio in the T-sites and the positional disorder accompanied by M-site vancancies. Annealing of the nonstoichiometric diffuse I¯1 anorthite in air at 1050 ° C for 14 days resulted in exsolution of minute SiO2 inclusions due to probable ordering in the T-sites and filling of M-sites by Ca. Stoichiometric P¯1 anorthite was not obtained by annealing at 1050 ° due to appreciable solubility of SiO2 in CaAl2Si2O8. Metastable hexagonal CaAl2Si2O8 was found to be a twinned monoclinic crystal with cell dimensions: a = 10.24 (2), b = 17.74 (3), c= 14.99 (5) Å, β = 92.05 (5) °, space group C2. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
