<p>Common (anhydrous) Fe-Mg-Ca-Mn garnet, the archetypal cubic mineral, has been recently discovered to be tetragonal in metapelites and metabasites from low-temperature regional metamorphic terranes (Cesare et al., 2018).</p><p>Despite the differences in bulk rock composition and pressure conditions, such low-T tetragonal garnets share common chemical features, namely high grossular (>25 mol%) and low pyrope (<7 mol%) contents. Similar compositions are documented in other contexts worldwide, both in blueschists-eclogites and in phyllites, including the metapelites from the garnet zone of the iconic Barrovian metamorphism of the Scottish highlands (Viete et al., 2011).</p><p>We have analysed a garnet crystal from a chlorite-biotite schist collected at the Barrow&#8217;s garnet zone in Glen Esk. The unit cell parameters were refined using diffraction reflections between 1.20 and 0.55 &#197; providing a tetragonal cell with a = 11.5731(5)&#160;&#197; and c = 11.5887(8)&#160;&#197; and volume V = 1552.15(15)&#160;&#197;3. Systematic absences analysis on complete intensity data collected up to 2theta = 80&#176; indicated I41/acd space group confirming the cell parameters refinement.</p><p>Therefore, the garnet is tetragonal and not cubic, as suggested by its weak birefringence under crossed polarizers.</p><p>These results show that the tetragonal structure of common Fe-Mg-Ca-Mn garnet is verified whenever this mineral displays the Ca-rich, Mg-poor composition often observed in low-T metamorphic rocks. And support the hypothesis that the lowering of symmetry is composition-dependent.</p><p>&#160;</p><p>References</p><p>Cesare, B., et al. Garnet, the archetypal cubic mineral, grows tetragonal. Sci Rep <strong>9</strong>, 14672 (2019).</p><p>Viete, D.R., et al. The nature and origin of the Barrovian metamorphism, Scotland: Diffusion length scales in garnet and inferred thermal time scales. J. Geol. Soc. London <strong>168</strong>, 115&#8211;132 (2011).</p><p>&#160;</p>