Along with significant flux incorporation, the material has several polytypic modifications, pictured in Figure , that might coexist in crystals. The calculated powder Xray diffraction patterns for each polymorph are difficult to distinguish, and they have virtually identical calculated formation energies in the Materials Project database. The R32 space group polymorph is most commonly realized for EuAl 3 (BO 3 ) 4 , but the C2 polymorph has been synthesized. For the third known RX 3 (BO 3 ) 4 polymorph, with C2/c space group symmetry, lattice parameters and domains within primarily R32 microcrystals have been reported for EuAl 3 (BO 3 ) 4 , but no bulk single crystal X-ray diffraction data or atomic positions were included. Reports about Eu/Al site mixing in the R32 polymorph also need addressing. Describing this array of potential defects is critical before collecting linewidth measurements.