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Clinopyroxene Group ABSi 2 O 6

Clinopyroxene Group ABSi 2 O 6. Presented by Joyleen Desai Paul Sandlin. Diopside. Hedenbergite. Acmite. Jadeite. Spodumene. Chemical Composition ABSi 2 O 6. Structural Cell Parameters. Monoclinic Space Group: C 2/ c Point Group: 2/ m. Source: http://webmineral.com. Structure.

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Clinopyroxene Group ABSi 2 O 6

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  1. Clinopyroxene GroupABSi2O6 Presented by Joyleen Desai Paul Sandlin

  2. Diopside Hedenbergite Acmite Jadeite Spodumene

  3. Chemical CompositionABSi2O6

  4. Structural Cell Parameters Monoclinic Space Group: C2/c Point Group: 2/m Source: http://webmineral.com

  5. Structure

  6. Thermal Expansion Source: Cameron et al. (1973)

  7. Compression Source: http://www.ciw.edu/schutt/depletion/depletion_intro.html

  8. Occurrences • Clinopyroxenes are found in mafic and ultramafic igneous rocks • They are also found in medium- to high-grade metamorphosed mafic rocks

  9. Metamorphic Facies Source: Spear (1995)

  10. Geothermobarometry • Inferring T and P • Thermodynamic modeling and calculations, electron microprobe • Assume equilibrium for sub-assemblages • Possible to infer PT conditions at various stages in rock history • Can’t find ages, but can construct PT time path

  11. Garnet-Cpx Thermobarometer Source: Spear (1995)

  12. Diopside-Enstatite Geothermometer • Below the solvus, a pyroxene of composition X will unmix to produce two pyroxenes • The degree of unmixing is a function of temperature Source: Perkins (1998)

  13. Crystal Structure

  14. Hydrous Sodic Cpx in the Upper Mantle Source: Smyth et al. (1991)

  15. Hydrous Importance • Cpx in eclogites as mantle samples • X-ray crystal structure refinement and analytical transmission electron microscopy (McCormick, 1996) • OH at dominant 3470 cm-1 band • O2 site is underbonded according to Pauling bond strength • M2 site is the most likely candidate for OH, 250-1840 ppm by weight • Cpx is stable at P=12 GPa, 30-400 km • Cpx is 5-10 times more abundant in mantle rocks

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