NDLI: Displacive phase transitions in C-centred clinopyroxenes: spodumene, LiScSi2O6 and ZnSiO3

Content Provider	Springer Nature Link
Author	Arlt, T. Angel, R. J.
Copyright Year	2000
Abstract	The clinopyroxenes spodumene (LiAlSi2O6), LiScSi2O6 and ZnSiO3, all with space group C2/c at ambient conditions, were studied under high pressures by single-crystal X-ray diffraction in a diamond-anvil cell. Changes in the evolution of the unit-cell parameters, optical properties and the appearance of h + k odd reflections characteristic of a primitive lattice, indicate that all three pyroxenes undergo phase transitions. The transitions are mostly displacive in character, and are non-quenchable. Transition pressures are 3.19 GPa in spodumene, ∼0.6 GPa in LiScSi2O6 and 1.92 GPa in ZnSiO3. The space group of all three high-pressure phases was determined to be P21/c by structure refinement to single-crystal X-ray intensity data collected in the DAC. In the ZnSiO3 clinopyroxene the intermediate P21/c phase further transforms to a second C2/c phase (HP-C2/c) at 4.9 GPa (confirmed by structure refinement). The volume change at this transition is about 2.6%, three times larger than in the first phase transition, and typical of the P21/c→ HP-C2/c phase transitions found previously in MgSiO3, FeSiO3, etc. These results therefore provide the first direct evidence that the HP-C2/c and the HT-C2/c structures of pyroxenes are distinct polymorphs with the same space group. The phase transition from C2/c to P21/c symmetry in spodumene and LiScSi2O6 therefore occurs because the polymorphs stable at ambient conditions are isotypic to the high-temperature C2/c phases of clinopyroxenes such as pigeonite and clinoenstatite.
Starting Page	719
Ending Page	731
Page Count	13
File Format	PDF
ISSN	03421791
Journal	Physics and Chemistry of Minerals
Volume Number	27
Issue Number	10
e-ISSN	14322021
Language	English
Publisher	Springer-Verlag
Publisher Date	2000-12-14
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Materials Science

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