In addition to flux inclusions, these crystals contain domains of multiple polymorphs. While stacking sequence defects are more common in simple metallic structures, they are also observed in oxides such as Ta 2 O 5 and TiO 2 where stacking sequences vary among polymorphs. The polymorphs of EuAl 3 (BO 3 ) 4 , similarly, are different stacking sequences of shared composition layers. Each polymorph contains AlO 6 octahedra, EuO 6 trigonal prisms, and BO 3 trigonal planes ar-ranged in one of three layer types Deviations from these sequences affect crushed crystals' powder XRD patterns, where asymmetric peaks appear, accompanied by an increase in the baseline at lower d-spacing. These peaks are prominent in synchrotron radiation powder XRD of R32 crystals grown from K 2 Mo 3 O 10 (Figure ). Three asymmetric peaks arise at d = 5.711 Å, 2.854 Å, and 1.958 Å. These values correspond well with the C2 polymorph's (110)/(1 10), (220)/(2 20), and (240)/(2 40) reflections. Based on calculated relative peak intensities for the C2 phase, one would expect additional but unobserved peaks, e.g. ( 2)/(1 12) and (1 13)/(113) reflections. The new peaks therefore likely stem from partially-formed monoclinic domains.