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The equation of state and stability of topaz at high-pressure/high-temperature conditions have been investigated by in situ synchrotron X-ray diffraction (<i>XRD</i>) and Raman spectroscopy in this study. No phase transition occurs on topaz over the experimental pressure–temperature (<i>P</i>-<i>T</i>) range. The pressure–volume data were fitted by the third-order Birch–Murnaghan equation of state (EoS) with the zero-pressure unit–cell volume <i>V</i>₀ = 343.86 (9) ų, the zero-pressure bulk modulus <i>K</i>₀ = 172 (3) GPa, and its pressure derivative <i>K</i>’₀ = 1.3 (4), while the obtained <i>K</i>₀ = 155 (2) GPa when fixed <i>K</i>’₀ = 4. In the pressure range of 0–24.4 GPa, the vibration modes of in-plane bending OH-groups for topaz show non-linear changes with the increase in pressure, while the other vibration modes show linear changes. Moreover, the temperature–volume data were fitted by Fei’s thermal equation with the thermal expansion coefficient <i>α</i>₃₀₀ = 1.9 (1) × 10⁻⁵ K⁻¹ at 300 K. Finally, the <i>P-T</i> stability of topaz was studied by a synchrotron-based single-crystal <i>XRD</i> at simultaneously high <i>P</i>-<i>T</i> conditions up to ~10.9 GPa and 700 K, which shows that topaz may maintain a metastable state at depths above 370 km in the upper mantle along the coldest subducting slab geotherm. Thus, topaz may be a potential volatile-carrier in the cold subduction zone. It can carry hydrogen and fluorine elements into the deep upper mantle and further affect the geochemical behavior of the upper mantle.