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Mineralogical Magazine; June 2006; v. 70; no. 3; p. 309-317; DOI: 10.1180/0026461067030334
© 2006 Mineralogical Society of Great Britain and Ireland
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On the thermo-elastic behaviour of kyanite: a neutron powder diffraction study up to 1200°C

G. D. Gatta1,*, F. Nestola2,3 and J. M. Walter4

1 Dipartimento di Scienze della Terra, Universita’ degli Studi di Milano, Via Botticelli, 23, I-20133 Milano, Italy
2 Bayerisches Geoinstitut, Universitaet Bayreuth, Universitaet Str. 30, D-95447 Bayreuth, Germany
3 Dipartimento di Mineralogia e Petrologia, Università degli Studi di Padova, Corso Garibaldi 37, I-35137 Padova, Italy
4 Mineralogisch-Petrologisches Institut, Universität Bonn, Forschungszentrum Jülich, D-52425 Jülich, Germany

* E-mail: diego.gatta{at}unimi.it

The high-temperature (HT) behaviour of kyanite (Al2SiO5) was investigated by in situ neutron powder diffraction up to 1200°C. Within the investigated T range, no phase transition was observed. The axial and volume thermal expansion coefficient ({alpha}j = lj–1({partial}lj/{partial}T), {alpha}V = V–1 ({partial}V/{partial}T)), calculated by weighted linear regression through the data points, are: {alpha}a = 5.5(2)x10–5, {alpha}b = 5.9(2)x10–5, {alpha}c = 5.18(8)x10–5, {alpha}V = 7.4(1)x10–3 °C–1, with {alpha}a:{alpha}b:{alpha}c = 1.06:1.14:1. All three angles of the kyanite lattice show a slight decrease with T, with {partial}{alpha}/{partial}T = –2(2)x10–5, {partial}ß/{partial}T = –4(1)x10–5, {partial}{gamma}/{partial}T = –10(2)x10–5°/°C. The magnitudes of the principal Lagrangian unit-strain coefficients ({varepsilon}1, {varepsilon}2, {varepsilon}3) and the orientations of the thermal strain-ellipsoids, between the ambient temperature and each measured T, were calculated. The magnitude and the orientation of all the three unit-strain coefficients are almost maintained constant with T. At T-T0 = 1177°C, {varepsilon}1{wedge}a = 76(2)°, {varepsilon}1{wedge}b = 70(2)°, {varepsilon}1{wedge}c = 38(3)°, {varepsilon}2{wedge}a = 49(3)°, {varepsilon}2{wedge}b = 66(3)°, {varepsilon}2{wedge}c = 127(4)°, {varepsilon}3{wedge}a = 135(3)°, {varepsilon}3{wedge}b = 31(3)°, {varepsilon}3{wedge}c = 91(2)° with {varepsilon}1: {varepsilon}2: {varepsilon}3 = 1.57:1.29:1. The structural refinements, performed at 23, 600, 650, 700, 750, 800, 900, 950, 1050 and 1200°C allowed the description of the structural evolution and the main T-induced deformation mechanisms, which are mainly represented by the polyhedral distortions of the AlO6 octahedra.

KEYWORDS: kyanite, Al2SiO5, neutron powder diffraction, high temperature, thermal behaviour




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G. D. Gatta, N. Rotiroti, and M. Zucali
Plastic deformations in kyanites by tectonometamorphic processes: a single-crystal X-ray diffraction study
Mineralogical Magazine, June 1, 2009; 73(3): 359 - 371.
[Abstract] [Full Text] [PDF]


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