Two independent reports in the literature for the elastic constants of zircon (zirconium silicate) are in disagreement by an order of magnitude and are reported without specifying the conditions of the mineralogical specimens. However, natural zircon crystals frequently contain uranium and thorium atoms as an impurity so that zircon can exist in a metamict (radiation damaged) condition. A redetermination of the elastic constants has been carried out on small synthetic crystals and on highhyphen;purity natural single crystals of nonmetamict zircon of lattice parametersaoequals; 6.606(2) Aring;,coequals; 5.980(2) Aring; by ultrasonic pulse superposition and also by phase comparison methods. The values in 1012dynsol;cm2arec11equals; 4.237,c33equals; 4.900,c44equals; 1.136,c66equals; 0.485,c12equals; 0.703, andc13equals; 1.495. The estimated uncertainty in the measurements are 0.4percnt; forc11,c33,c44, andc66, and 3percnt; forc12andc13. Wave velocity measurements have also been carried out on a metamict zircon crystal (density 4.531 gsol;cm3) and it is shown that the velocities are reduced by about onehyphen;fifth the normal values. The compressibility coefficients calculated from the new elastic constants data differ from those determined by diffraction data, though this may be part of a general discrepancy between such measurements.
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