Cell parameters of thermally treated anorthite. Al,Si configurations in the average structures of the high temperature calcic plagioclases |
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Authors: | Piera Benna Giorgio Zanini Emiliano Bruno |
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Affiliation: | (1) Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via San Massimo 22, I-10123 Torino, Italy |
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Abstract: | Thermal treatments of anorthite carried out at up to 1,547° C show that the unit cell parameter changes as a function of the treatment temperature. The best fit curve found by non-linear least squares analysis is: =91.419-(0.327·10-6)T2+(0.199·10-12)T4-(0.391·10)T6. The results obtained support significant Al,Si disorder (Al0.10, where Al=t1(0)-1/3 [t1(m)+t2(0)+t2(m)], Ribbe 1975), in anorthite equilibrated near the melting point and confirm a high temperature series differentiated from the low temperature series for calcic plagioclases in the An85–An100 range also. In the plot vs. An-content the high and low temperature curves intersect at An85 composition and progressively diverge in the An85–An100 range. The trends of the high and low temperature curves in this range are interpretable on the basis of the degree of Al, Si order in the average structures of calcic plagioclases. |
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