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| Titel |
Thermal Expansion of Fluorapatite-Chlorapatite Solid Solutions |
| VerfasserIn |
Guy Hovis, Tony Abraham, William Hudacek, Sarah Wildermuth, Brian Scott, Caitlin Altomare, Aaron Medford, Maricate Conlon, Matthew Morris, Amanda Leaman, Christine Almer, Gary Tomaino, Daniel Harlov |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102512
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| Publikation (Nr.) |
 EGU/EGU2015-1835.pdf |
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| Zusammenfassung |
| X-ray powder diffraction experiments have been performed on fifteen fluorapatite-chlorapatite
solid solutions synthesized and chemically characterized at the GeoForschungsZentrum -
Potsdam (Hovis and Harlov, 2010; Schettler, Gottschalk, and Harlov, 2011), as well as two
natural near-end-member samples, from room temperature to ~900 °C at 50 to 75 °C
intervals. NIST 640a Si was employed as an internal standard; data from Parrish (1953) were
used to determine Si peak positions at elevated temperatures. Unit-cell parameters calculated
using the software of Holland and Redfern (1997) result in volume-temperature (V-T) plots
that are linear or slightly concave up (V plotted as the vertical axis) over the T range
investigated. Relations for the "a" and "c" unit-cell dimensions with T for these hexagonal
minerals are nearly linear, but as with V, commonly improved by quadratic fits to the
data. Coefficients of thermal expansion for volume (αV ), calculated as (1/V0°C) x
(δV/δT) based on linear V-T relationships, mostly fall within the range 42 ± 2 x
10-6 deg-1 and show no obvious dependence on composition. Thermal expansion
coefficients for individual unit-cell axes, however, do show clear relationships to
composition, αa increasing from ~9.5 to ~13.5 x 10-6 deg-1 and αc decreasing
from ~19.5 to ~13 x 10-6 deg-1 from the Cl to the F end member. Clearly, a
compensating structural relationship accounts for the observed relationships. Such
compositional dependence was not seen in the thermal expansion data for F-OH
apatite solid solutions (Hovis, Scott, Altomare, Leaman, Morris, and Tomaino,
American Mineralogist, in press). This difference can be explained by the similar
sizes of F- and (OH)- versus the much greater size contrast between F- and Cl-.
Sincere thanks to the National Science Foundation for support of this work, which has
provided numerous research experiences for Lafayette College undergraduates. Thanks
also to the Earth Sciences Department, University of Cambridge, for providing
X-ray facilities for a portion of these measurements. Finally, thanks to Jeff Post,
National Museum of Natural History, and George Harlow, American Museum of
Natural History, for providing the natural fluorapatite (NMNH 144954-3, Durango,
Mexico) and chlorapatite (AMNH 23101, Kragero, Norway) samples, respectively. |
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