Chemical equilibrium calculations performed at p = 110 dyne cm⁻² and with the software GGchem (Woitke et al. 2018) for a large gas-phase mixture with 865 species and including clusters of (Al₂O₃)_n, n =1−10 (top); (MgAl₂O₄)_n, n = 1−7 and (Al₂O₃)_n, n = 1−10 (second row); (Mg_xCa_1−xAl₂O₄)_n, x∊ (0..1], (MgAl₂O₄)_n, n =1−7, and Al₂O₃)_n, n = 1−10 (third row); and (CaAl₂O₄)_n, (Mg_xCa_1−xAl₂O₄)_n, x∊(0,1], (MgAl₂O₄)_n, n = 1−7, and (Al₂O₃)_n, n = 1−10 (bottom).