Abstract
The structures of natural and synthetic* α-eucryptites, LiAlSiO4, are trigonal with space group R[unk], a = 13.471(3) [13.473(3)]Å, c = 8.998(2) [9.001(2)] Å, Z = 18, Dx = 2.66 [2.66] gcm−3. They were refined to R (unweighted) = 0.055 [0.054] and R (weighted) = 0.043 [0.041] using 1721 [1710] non-equivalent reflections. The structures consist of [LiO4] tetrahedra (mean Li – O distance 1.982 [1.983] Å) and [TO4] tetrahedra with T = Al/Si (mean T – O distance 1.688 [1.688] Å). It is confirmed that α-eucryptite, natural and synthetic, is isostructural with phenakite and willemite, and has a three-dimensional tetrahedral framework. The Li atoms of eucryptite occupy the sites equivalent to the Si positions in phenakite and willemite. The Al and Si atoms of eucryptite are disordered in the sites equivalent to the Be and Zn positions in phenakite and willemite.
