# Equations of state of Plagioclase Feldspars

Original Paper

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## Abstract

The volume variation with pressure of seven intermediate plagioclase feldspars has been determined by high-pressure single-crystal X-ray diffraction. The bulk moduli of plagioclases for a 3rd-order Birch-Murnaghan EoS can be described by the following pair of equations: with \({K}'_{0} = 5.8\) for plagioclase with

$$ K_{{T0}} = 54.1{\left( 3 \right)} + 0.39{\left( 1 \right)}X_{{An}} {\text{ for }}X_{{An}} < {\text{50}} $$

$$ K_{{T0}} = 59.5{\left( {3.1} \right)} + 0.23{\left( 4 \right)}X_{{An}} {\text{ for }}X_{{An}} > {\text{50}} $$

*X*_{ An }<20 and \({K}'_{0} = 3.2\) for*X*_{ An }>35. These parameters can also be used in a Murnaghan EoS to describe the volume variation of plagioclase feldspars up to pressures of 3 GPa. For a Murnaghan EoS with \({K}'_{0} = 4\), the values of the bulk moduli can be described by a single equation, \( K_{{T0}} = 57.7{\left( 6 \right)} + 0.24{\left( 1 \right)}X_{{An}} \), with a small loss in the accuracy of the predicted volumes up to pressures of 3 GPa.## Keywords

Bulk Modulus Finite Strain Thermodynamic Database Bulk Modulo Plagioclase Feldspar
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

## Notes

### Acknowledgements

Michael Carpenter generously donated the samples and provided details of some unpublished electron microprobe and TEM analyses, and Patrick O’Brien analyzed sample 67783. The X-ray diffraction data was collected while the author was a member of the Bayerisches Geoinstitut in Bayreuth. Data analysis was supported by NSF grant EAR-0105864 to NL Ross and RJ Angel at Virginia Tech.

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