Cracking Quartz: What this Phase Transition Means for Seismic Studies

Quartz isn’t just one of the most common mineral—it plays a crucial role in shaping the Earth’s crust. At high temperatures and pressures, quartz undergoes a phase transition from its usual trigonal (alpha) form to a hexagonal (beta) form, significantly changing its thermodynamic and elastic properties. Scientists believe this transformation contributes to seismic velocity contrasts detected in the Earth’s crust. But how well do current models capture this transition?

In this study, Giulia Mingardi and co-authors put quartz to the test under high-pressure and high-temperature (HP-HT) conditions using synchrotron X-ray diffraction and acoustic measurements. They measured seismic wave velocities (Vp and Vs) and key elastic properties like the adiabatic bulk modulus (Ks) and shear modulus (G).

Their data aligns with existing thermodynamic models, meaning quartz-inclusion pressures calculated via elastic barometry should be reliable.

Their measured Vp, Vs, and Ks for beta-quartz were significantly lower than predicted values.

This discrepancy suggests that seismic interpretations of beta-quartz in the lower crust need to be handled with caution.

This study reinforces that while current models work well for certain conditions, understanding beta-quartz in the deep crust remains a challenge. This has big implications for seismic studies and interpretations of quartz inclusions—reminding us that even well-known minerals still hold mysteries!