• journal_title：Mineralogical Magazine
• Contributor：S. J. Mills ; F. Nestola
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2012.076.4.13
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：76
• issue：4
• firstpage：975
• section：Articles

Arsenoflorencite-(La), ideally LaAl₃(AsO₄)₂(OH)₆, was studied at high pressure by single-crystal X-ray diffractometry. The unit cell was determined at nine pressures up to 7.471(8) GPa; no evidence of a phase transformation was found in this range. The pressure–volume data (refined simultaneously) were fitted to a third-order Birch–Murnaghan equation of state which gave V₀ = 710.71(8) ų, K_T0 = 106(2) GPa and K′ = 9.2(9). These values were confirmed independently from an F_E–f_E plot. The crystal structure was refined at 1.596, 3.622, 5.749 and 7.471 GPa, the first time this has been done for a member the alunite supergroup. The compressibility of arsenoflorencite-(La) is strongly anisotropic, with β_c > β_a. The main compression mechanism was found to be governed by the internal angle O3–La–O2 of the La polyhedron, where the O2 and O3 atoms move toward the c axis during compression.