Elastic Properties of Iron-Bearing Olivine
Mentor:Donald Isaak, Professor of Physics, Azusa Pacific University
We are using a technique known as resonant ultrasound spectroscopy (RUS) to determine the elastic properties of a crystal known as olivine at high temperature. This technique requires cutting and grinding a crystal into a right-rectangular parallelepiped with faces along its crystallographic axes. The prepared specimen is then placed between two transducers that are connected to a frequency generator which passes a range of sinusoidal frequencies through the crystal. The first transducer introduces the signal to the crystal while the second is used to determine the crystal response. The data are then analyzed for the resonant frequencies which are used to determine the elastic properties of the crystal. This process is first done at room temperatures and then repeated at higher temperatures. RUS elasticity measurements have been published for several other crystals and are used to help determine the composition of Earth’s interior by comparing these laboratory measurements with profiles of Earth interior from seismic studies. We are using a synthetic olivine crystal that is 20% iron and 80% magnesium silicate. Previous results have been published on 10% iron olivine. We hope to determine the effect iron has on the elastic constants and their temperature dependences. This summer we carefully measured the density of the crystal to estimate its composition, cut and polished the crystal along its axes, passed frequencies through at room temperatures to map out the resonant frequencies, and varied the holding force on the crystal to predict the frequency with zero holding force. Our next step is to calculate the elastic constants and then repeat the process at higher temperatures so as to determine the temperature dependence of the elastic constants.