• journal_title：American Mineralogist
• Contributor：Marcus J. Origlieri ; Robert T. Downs ; Richard M. Thompson ; Carolyn J.S. Pommier ; M. Bonner Denton ; George E. Harlow
• Publisher：Mineralogical Society of America
• Date：2003-
• Format：text/html
• Language：en
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：88
• issue：7
• firstpage：1025
• section：Articles

The crystal structure of synthetic kosmochlor, NaCrSi₂O₆, was studied using single crystal X-ray diffraction at high pressure. A four-pin diamond anvil cell, with 4:1 methanol:ethanol pressure medium, was used to achieve pressures to 9.28 GPa. Unit-cell data were collected at 20 pressures, and intensity data were collected at 13 of these pressures. Fitting the P-V data to a third-order Birch-Murnaghan equation yields V₀ = 418.84(3) ų, K₀ = 134(1) GPa⁻¹, and K₀′ = 2.0(3). Anisotropic compression was observed with unit strain axial ratios of 1:1.82:2.08. The CrO₆ octahedron has a bulk modulus K₀ = 90(16) GPa⁻¹, while the SiO₄ tetrahedron has K₀ = 313(55) GPa⁻¹, both with K₀ ′ ≡4. An o-type rotation of the O3-O3-O3 linkage was observed with pressure, with ∠O3-O3-O3 decreasing from 172.8(2)° to 166.1(7) °. Compression in kosmochlor is related to the stacking directions of distorted cubic closest packed O atom monolayers. Unit strain ellipsoids for diopside, hedenbergite, spodumene (C2/c and P2₁/c), LiScSi₂O₆ (C2/c and P2₁/c), clinoenstatite, orthoenstatite, and Mg_1.54Li_.23Sc_.23Si₂O₆ (Pbcn and P2₁cn) were generated and discussed in terms of closest packing systematics. A relationship between the anisotropy of compression of olivines and pyroxenes is established. A strategy to determine not only the direction of a stress field in deformed rocks, but also an estimate of the magnitude of stress is discussed in terms of comparing the anisotropy of olivine and pyroxene.