The crystal structure of Sr7ZrSi6O21 is described. Sr7ZrSi6O21, M(r)=1209.10, triclinic, P1BAR, a=8.398(3)angstrom, b=8.435(2)angstrom, c=8.445(3)angstrom, alpha=106.13(3)-degrees, beta=106.49(3)-degrees, gamma=105.90(3)-degrees, V=509.0(3)angstrom3, Z=1, D(x)=3.944(3)Mgr/m3. Lambda(MoKalpha)=0.71069angstrom, F(000)=558, room temperature, final R=0.073 for 1145 observed reflections. The structure is pseudo rhombohedral, R3BAR, a(hex)=13.474angstrom, c(hex)= 9.714angstrom, Z=3. The crystal structure determination establishes the formula for the compound earlier described in phase equilibria studies as Sr6ZrSi5O18.