Elastic constants of nonmetamict zirconium silicate

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Abstract
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 high‐purity natural single crystals of nonmetamict zircon of lattice parameters ao = 6.606(2) Å, co = 5.980(2) Å by ultrasonic pulse superposition and also by phase comparison methods. The values in 1012 dyn/cm2 are c11 = 4.237, c33 = 4.900, c44 = 1.136, c66 = 0.485, c12 = 0.703, and c13 = 1.495. The estimated uncertainty in the measurements are 0.4% for c11, c33, c44, and c66, and 3% for c12 and c13. Wave velocity measurements have also been carried out on a metamict zircon crystal (density 4.531 g/cm3) and it is shown that the velocities are reduced by about one‐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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