The pressure and temperature dependence of the elastic constants of pyrope garnet

Abstract

This paper reports the ultrasonic measurements of the single‐crystal second‐order elastic constants and their pressure and temperature derivatives for a natural sample of pyrope garnet of composition (Mg0.61, Fe0.36, Ca0.02)3Al2Si3O12. Within the experimental precision of the pulse superposition method the pressure and temperature dependences of each of the three independent elastic constants were found to be linear in the range up to 10 kbar and from ambient conditions to 100°C. The pertinent results for the adiabatic bulk modulus are K0s = 1682.1 ± 3.6 kbar, (∂Ks/∂P)T = 4.74 ± 0.16, and (∂Ks/∂T)P = −0.188 ± 0.006 kbar/°C, where each parameter is evaluated at 1 bar and 25°C. These results are generally consistent with previous studies of the elasticity of pyrope garnet using high‐pressure static compression methods; however, the present data have the advantage of increased precision and accuracy. In addition, comparison of our results with corresponding data for other (Mg, Fe, Mn, Ca)3Al2Si3O12 garnets suggests that the specific type of the divalent cation in the eightfold coordination site has a relatively minor effect on the elastic properties of garnet, except for the Ca‐rich end‐member, grossularite.

Compressions of synthetic pyrope, spessartine and uvarovite garnets up to 25 GPa

“…Unfortunately, there are no available data to calculate in the same way the B'o value for pure end-member pyrope, uvarovite and spessartine garnets. However, this value range is in good agreement with the experimental values, 5.4 and 4.74_+0.16, determined by Soga (1967) and Bonczar and Graham (1977) from acoustic experiments which were conducted on natural samples over a pressure range limited to 1 GPa or with a very recent value 4.93 for a natural red blood pyrope (Webb 1989).…”

Elasticity of single-crystal iron-bearing pyrope up to 20 GPa and 750 K

“…4 and 5 and Table 2) (Verma, 1960;Soga, 1967;Bonczar et al, 1977;Leitner et al, 1980;Webb, 1989;O'Neill et al, 1991;Chen et al, 1997Chen et al, , 1999Conrad et al, 1999;Sinogeikin and Bass, 2000;Wang and Ji, 2001;Jiang et al, 2004;Gwanmesia et al, 2006Gwanmesia et al, , 2007. Here the potential effect of Ca and Mn on the elasticity of pyrope is not considered because of their limited amounts in the studied samples.…”

“…We have also compared the temperature derivatives of the bulk and shear moduli in Fe-bearing pyrope to the literature results (Table 3) (Soga, 1967;Bonczar et al, 1977;Sumino and Fig. 2.…”

High-temperature thermal expansion and elasticity of calcium-rich garnets

“…Relatively fewer data are available on the temperature dependence of the elastic properties of garnets, which is the focus of our study. The temperature dependence of elasticity has been reported for almandine-spessartine (Feo.s2 ,Mno.46 ,Ca0.ol)3A12Si3012 (Isaak and Graham 1976), pyrope-almandine (Mg0.61 , Feo.36, Cao.02)3AlzSi3012 (Bonczar and Graham 1977), and three specimens of predominantly pyrope and almandine (Sumino and Nishizawa 1978). All of these derivatives are evaluated at ambient conditions based on data obtained over the temperature range 300-475 K. Two earlier sets of data on temperature derivatives of elasticity (Reddy and Bhimasenachar 1964;Soga 1964) include some values which appear to be anomalous (Sumino and Nishizawa 1978).…”