Ferrous tainiolite, CsFe2LioSi4tO10F2, has been synthesized from the melt in gastight molybdenum crucibles. The electric conductivity has been measured by impedance spectroscopy. As compared to natural micas, which are insulators, good conductivity is observed. The layered silicate can be further modified by ion exchange, which makes it a promising host structure for sensor materials. The estimated activation energy is as low as 0.79 eV. Upon Ba2exchange for Cs, structural Fe2is partially oxidized (33%), and the layer charge is reduced significantly, resulting in a coarse-grained but swollen (monolayer hydrate) smectite-type layered silicate. Therefore, further functionalization by pillaring will be feasible resulting in a conducting microporous material. The new material has been characterized by the analysis of chemical composition (wavelength dispersive X-ray spectroscopy and laser ablation-inductively coupled plasma−mass spectrometry), differential thermal analysis, electron microscopy, Mössbauer, UV−vis/NIR, impedance spectroscopy, and single-crystal structure refinement (wR(F2) 0.0883). The structure is of the 1Mpolytype (C2/m) with cell parameters a5.277(2) Å, b9.148(2) Å, c10.804(2) Å, and 99.19(3)°. The congruent melting point was observed at 1103 (±5) K. [ABSTRACT FROM AUTHOR]