Computer Science
Scientific paper
Jul 1970
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970e%26psl...8..448p&link_type=abstract
Earth and Planetary Science Letters, Volume 8, Issue 6, p. 448-450.
Computer Science
3
Scientific paper
Cummingtonite from the Gouverneur, New York, talc district (Sample No. U.S.N.M. 115046) with the composition, (Ca0.36Na0.06Mn0.96Mg0.57) Mg5Si8O22 (OH)2, unit cell parametersa = 9.550 ± 0.001, b = 18.007 ± 0.003, c = 5.298 ± 0.001Å, β = 102°39′ ± 1′, and space groupP21/m, has been used in a high-temperature, single-crystal, X-ray diffraction study. When diffraction patterns are taken of the crystals heated in a sealed silica capillary to 45°C or higher, these reflections disappear, indicating a transition toC2/m symmetry. The transition appears to be analogous to theP21/ctoC2/c transition between 700° and 800°C discovered recently in (Mg0.30Fe0.70) SiO3 clinopyroxene.In addition to the cummingtonite transition, we have also found a transition in pigeonite at higher temperatures. The transition occurs in this pigeonite (Gunflint Iron Formation, Minnesota, (Ca0.04Fe0.78Mg0.18)SiO3) at about 670°C. This is a significantly lower temperature than was found for the Ca-poor clinopyroxene.
Papike James J.
Prewitt Charles T.
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