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This content will become publicly available on January 17, 2026

Title: Thorite: An Oddity in Phase Stability Amongst the Zircon-Structured Orthosilicates at High Pressures
Abstract Synthetic thorite and huttonite, two polymorphs of ThSiO4, were investigated by a combination of in situ high-pressure synchrotron X-ray powder diffraction and in situ high pressure Raman spectroscopy. The average onset pressure of the thorite-to-huttonite transition was determined to be 6.6 ± 0.2 GPa, using both techniques. The bulk moduli of thorite and huttonite were determined to be 139(9) and 246(11) GPa, respectively, by fitting their unit-cell volume data to a second order Birch-Murnaghan equation of state (EOS). Based on its bulk modulus, thorite is the most compressible zircon-structured orthosilicate, as it has the largest unit cell volume among tetravalent metal orthosilicates. The pressure derivatives of the vibrational modes of thorite were found to be consistent with those previously reported for other orthosilicates (e.g., zircon, hafnon, stetindite, and coffinite), while having the smallest Grüneisen parameter. A new P-T phase diagram for ThSiO4 is proposed, where the boundary of the thorite → huttonite transition is: P(T) = (7.8 ± 0.9 GPa) − (0.006 ± 0.002 GPa/K)T. Based on the new P-T phase diagram, we further estimated the enthalpy of formation of huttonite, ΔHf,ox, to be 0.6 ± 6.0 kJ/mol, suggesting its metastability and rare locality in nature.  more » « less
Award ID(s):
2149848 2144792 2112653
PAR ID:
10577765
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
degruyter
Date Published:
Journal Name:
American Mineralogist
ISSN:
0003-004X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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