Synthesis of aenigmatite

Abstract

Aenigmatite with the formula Na₄[Fe₁₀²⁺Ti₂]Si₁₂O₁₄ has been synthesized hydrothermally, at 700 °C and 1000 bars P_{H2O, 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.}