Compressibility of synthetic potassium-rich clinopyroxene: In-situ high-pressure single-crystal X-ray study

Luca Bindi, Robert T. Downs, George E. Harlow, Oleg G. Safonov, Yuriy A. Litvin, Leonid L. Perchuk, Hinako Uchida, Silvio Menchetti

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9 Scopus citations


The crystal structure of a synthetic potassium-rich clinopyroxene, (Ca0.88K0.12)(Mg0.83Al0.17) (Si1.98Al0.02)O6, was studied using high-pressure single-crystal X-ray diffraction methods. A four-pin diamond anvil cell with 4:1 methanol:ethanol pressure medium was used to achieve pressures to 9.72 GPa. Unit-cell data were measured at 17 pressures, and intensity data were collected at 6 pressures. Fitting the P-V data to the third-order Birch-Murnaghan equation of state yields V0 = 435.49(3) Å3, K0=129(1) GPa, K' = 2.7(3). Anisotropic compression was observed with unit strain axial ratios of 1:1.94:1.90. Unit-cell parameters decrease gradually as a function of pressure with axial compressibilities βb > βc ∼ βa. They match those found for kosmochlor but are stiffer than those observed for synthetic diopside and hedenbergite. Compressibilities of the bond distances within the M2, M1, and T polyhedra show significant anisotropy. The incorporation of K into the clinopyroxene structure has little effect on its compressibility, although the concomitant substitution of Al in M1 from the K-Jd component reduces its compressibility. The K atom is softer than the M2 polyhedron and thus shrinks enough at high pressure to fit into the pyroxene structure.

Original languageEnglish (US)
Pages (from-to)802-808
Number of pages7
JournalAmerican Mineralogist
Issue number5-6
StatePublished - 2006


  • Chemical mineral analysis
  • Clinopyroxene
  • Crystal structure
  • High-pressure studies
  • XRD data

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology


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