Summary: Aenigmatite with the formula Na4[Fe102+Ti2]Si12O40 has been synthesized hydrothermally, at 700 °C and 1000 bars PH2O, from an oxide starting material. The oxygen fugacity was controlled by means of an iron-wüstite buffer. An indexed X-ray powder pattern of synthetic aenigmatite is given, together with comparative data on two natural samples. One of the aenigmatites, from Kola, U.S.S.R., is known to be triclinic (Kelsey and McKie, 1964). The powder patterns of this and the synthetic aenigmatite are so similar that it is concluded that the latter is also triclinic, at least at room temperature.