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The geometric effects of VFe2+ for VMg substitution on the crystal structures of the grandidierite-ominelite series by T. J. Dzikowski; L. A. Groat; E. S. Grew is a Earth and Planetary Sciences article available to read on EtoBox.

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The electron microprobe compositions and crystal structure of seven members of the grandidierite-ominelite (MgAl 3 BSiO 9 -Fe 2+ Al 3 BSiO 9 ) series with X = (Fe 2+ + Mn + Zn)/(Fe 2+ + Mn + Zn + Mg) ranging from 0.00 to 0.52 were studied to determine the geometric effects of Fe substitution for Mg on the crystal structures. Calculating Fe 3+ from the electron microprobe analyses gave 0.04-0.06 Fe 3+ apfu, but such small amounts at the Al sites could not be detected in the reÞ nements. Regression equations derived from single-crystal X-ray diffraction data show that b increases by 0.18 Å from X = 0-1. The crystal structure reÞ nements show that the most signiÞ cant changes involve the (Mg,Fe 2+ )O 5 polyhedron, which increases in volume by 0.36 Å 3 (5.0%), largely as a result of expansion of the MgFe-O5, -O2, and -O6 (×2) bond distances, which increase by 0.09 (4.4%), 0.06, and 0.04 Å, respectively. Other signiÞ cant changes include increasing O1-MgFe-O2 (3.44°) and -Al3-O5a angles (1.9°) and a decreasing O6-MgFe-O6b (-2.20°) angle. SigniÞ cant increases are also seen in the lengths of the O1-O2 (0.13 Å) and O6-O5a (×2) (0.09 Å) edges. The SiO 4 tetrahedra appear to respond to chan

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Author

T. J. Dzikowski; L. A. Groat; E. S. Grew

Publisher

Mineralogical Society of America

Published

2007

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)