Title: Elasticity of enstatite and its relationship to crystal structure
Abstract: The nine adiabatic single‐crystal elastic moduli of a natural orthopyroxene of enstatite composition (Mg 0.94 Fe 0.06 SiO 3 ) have been measured at ambient conditions by Brillouin spectroscopy. The single‐crystal elastic stiffnesses in gigapascals (GPa) are C 11 = 229.3 ± 1.1; C 22 = 167.0 ± 1.1; C 33 = 193.9 ± 1.5; C 44 = 79.7 ± 0.7; C 55 = 76.1 ± 0.6; C 66 = 77.1 ± 0.9; C 12 = 73.6 ± 1.7; C 13 = 49.8 ± 1.6; and C 23 = 46.6 ± 1.6. The average Hashin‐Shtrikman bulk and shear moduli are 102.2 and 73.9 GPa, respectively. The results of this study are generally consistent with those obtained for other Mg‐rich pyroxenes. Some of the individual moduli along the enstatite‐ferrosilite join can be related to specific chemical and structural features. The most variable modulus is C 33 , and it appears to be a complicated function of both chemistry and structure. Its magnitude relative to C 11 is most easily explained by the presence or absence of more than one tetrahedral chain. For orthopyroxenes of intermediate composition C 11 is higher than expected, probably due to a combination of the effects of site ordering and impurities in the Ml site. The third longitudinal modulus, C 22 , is observed to increase linearly as a function of enstatite composition from En 0 to En 100 . An alternative interpretation for C 11 and C 22 is that between En 100 and En 50 , C 11 is constant and C 22 decreases linearly with increasing iron content, while between En 50 and En 0 , C 11 decreases linearly and C 22 is constant. The shear and off‐diagonal moduli vary nonsystematically but tend to vary in similar ways. With the exception of C 12 , the averaged moduli also show nonsystematic variations. Cation site ordering appears to strongly affect C 44 . The modulus C 11 is also nonsystematic but for reasons which are not obvious. Our results are consistent with the interpretation that the bulk modulus does not vary with composition whereas the shear modulus does so in a linear fashion.
Publication Year: 1988
Publication Date: 1988-01-10
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 287
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