**5. Experimental physical acoustics and elasticity of minerals**

Experimental physical acoustics has been used to study the elastic properties of minerals. These high-precision techniques provide measurements of the velocity of sound in single crystals or polycrystalline aggregates (i.e., rocks) as functions of pressure and temperature.

There are several goals of such research in geophysics:


Our recent paper [8] summarizes the current state-of-the-art in studies of the Earth's interior using measurements of sound velocities in minerals by ultrasonic interferometry. In that paper, we reviewed the progress of the technology of ultrasonic

### **Figure 9.**

*Comparison of seismic models (PREM-dashed lines and AK135-solid lines) with possible mineral phase transitions in the minerals of the upper mantle (see also Figures 3 and 7a, b).*

### **Figure 10.**

*The progress in the pressures and temperatures achievable in these investigations using laboratory acoustics from 1994 to 2014 is reflected in these three figures.*

interferometry from the early 1950s to the present day. During this period of more than 60 years, sound wave velocity measurements have been increased from pressures less than 1 GPa and temperatures less than 800 K to conditions above 25 GPa and temperatures of 1800 K. This is complimentary to other direct methods to measure

### *Mineral Physics DOI: http://dx.doi.org/10.5772/intechopen.102326*

sound velocities (such as Brillouin spectroscopy and impulsive stimulated scattering) as well as indirect methods (e.g., resonance ultra- sound spectroscopy, static or shock compression, inelastic X-ray scattering). Newly-developed pressure calibration methods by Wang *et al*. [9] and data analysis procedures using a finite strain approach are described and applied to data for the major mantle minerals. These state-of-theart ultrasonic experiments performed in conjunction with synchrotron X-radiation provide simultaneous measurements of the elastic bulk and shear moduli and their pressure and temperature derivatives with direct determination of pressure.

These sound velocity data are important in enabling scientists to interpret seismic data for the Earth's interior. Two of the most popular global seismic models are PREM and AK135 [10, 11] are plotted in **Figure 9**; these models include some distinct features including a low velocity zone around 80 km–150 km, jumps at 410- and 670-km depths, and high velocity gradients in the transition zone. In addition, regional seismic studies also revealed discontinuities at 520 km as well as at depths of 250 km–340 km (X discontinuity). Also plotted are phase transitions as possible causes of these velocity anomalies in a pyrolytic mantle compositional model (See **Figure 9** and **Figures 3** and **7a** and **b** above).

The progress in the pressures and temperatures achievable in these investigations using laboratory acoustics from 1994 to 2014 is reflected in the following figures (**Figure 10**); copyright R. C. Liebermann.

## **6. Current status of mineral physics research**

In early 2019, I wrote a paper entitled "The Orson Anderson Era of Mineral Physics at Lamont in the 1960s", and began to explore options for its publication. When the Assistant Editor for Minerals, Ms. Jingjing Yang, agreed to consider my paper, she also inquired as to whether I would like to the be the Guest Editor for a Special Issue in honor of Orson Anderson. After asking prospective authors about the viability of such a Special Issue, I accepted her invitation, with the hope and expectation that it would be a wonderful present for his 95th birthday. This Special Issue is the result [12]. It contains original scientific papers, as well as historical reviews of the field of mineral physics (and also rock physics).

The papers in this Special Issue are grouped into four categories: Reviews, Experimental Science, Theoretical Science and Technological Developments. These papers include those from; first authors covering five generations of mineral physicists, including contemporaries of Orson, the next generation of leaders in mineral physics throughout the world, current leaders in the field, senior graduate students, and an undergraduate student (i.e., Tyler Perez). Note that Tyler, a student of Jennifer Jackson at Caltech, is an academic great-great grandson of Orson Anderson (Anderson > Liebermann > Bass > J. Jackson > Perez).

Examples of papers in all four categories of the Special Issue [12]:

## **7. Review**

William A. Bassett.

The Takahashi–Bassett Era of Mineral Physics at Rochester in the 1960s. Reprinted from: Minerals 2020, 10, 344, doi:10.3390/min10040344
