Thermal expansion of minerals in the pyroxene system and examination of various thermal expansion models

Tomaino, G.; Tribaudino, M.; Hovis, Guy L.; Almer, C.; Altomare, C.; Morris, D.; Jackson, K.; Leaman, A.; Scott, B.; Morris, M.; Mantovani, L.; Maksymiw, N.

Thermal expansion of minerals in the pyroxene system and examination of various thermal expansion models

Abstract

To examine the effects of chemical composition on thermal expansion in the pyroxene mineral group, X-ray diffraction data have been collected from room temperature to similar to 925 degrees C on a chemically diverse group of 13 pyroxenes including four orthorhombic and nine monoclinic samples. Additionally, resulting unit-cell volumes computed from the XRD data have proven to be good tests for a large number of thermal expansion models; the physical model by Kroll and coworkers and the empirical one by Fei have been found to be especially useful. Modeling also has allowed the connection of present data, collected at temperatures above 25 degrees C, to the volume data of other workers for much lower temperatures, well below 0 degrees C, and also extrapolation of values for volume and thermal expansion well beyond the measurement range.

We have found for orthopyroxenes that Fe2+-Mg2+ substitution has little effect on thermal expansion coefficients for volume. For clinopyroxenes, however, greater thermal expansion occurs in Ca2+- (diopside, augite, hedenbergite, johannsenite) than in Li+- (spodumene) or Na+-bearing members (jadeite, aegirine, kosmochlor). Present data support the observation that differences in volume thermal expansion relate primarily to differences in expansion along the b crystallographic axis. This apparently is due to the greater concentration of M1 polyhedra along the b crystallographic axis, where expansion differences can be related to the shared O1-O1 polyhedral edge and inter-oxygen repulsion that is made easier by divalent, as opposed to trivalent, cation occupancy of the M1 crystallographic site.

Title	Thermal expansion of minerals in the pyroxene system and examination of various thermal expansion models
Creator	Tomaino, G.
	Tribaudino, M.
	Hovis, Guy L.
	Almer, C.
	Altomare, C.
	Morris, D.
	Jackson, K.
	Leaman, A.
	Scott, B.
	Morris, M.
	Mantovani, L.
	Maksymiw, N.
Publisher	American Mineralogist
Academic Department	Geology & Environmental Geosciences
Division	Natural Sciences
Organization	Lafayette College
Date Issued	June 1, 2021
Date Available	2022-06-07
Type	Article
Language	English
Keyword	Modeling
	Pyroxenes
	Thermal expansion
Bibliographic Citation	Hovis, G. L., et al. (2021 June 1) "Thermal expansion of minerals in the pyroxene system and examination of various thermal expansion models." American Mineralogist 102 (6): 883-899.
Standard Identifier	DOI 10.2138/am-2021-7650
Standard Identifier	Handle 10385/sx61dn76r
Permalink	http://hdl.handle.net/10385/sx61dn76r
Rights Statement	In Copyright
Rights Holders	Mineralogical Society of America