Mica gaskets and also composite gaskets containing compressive mica interlayers are under consideration as sealing materials in solid oxide fuel cells (SOFC). To study potential interactions between the interconnect steel Crofer22APU and the mineral phases vermiculite (exfoliated) (K, Mg, Fe) 3(Si, Al) O-4(10)(OH)(2)) and talc (Mg3Si4O10(OH)(2)), corrosion experiments were conducted in simulated SOFC conditions. The opposite walls of the gaskets were simultaneously exposed to air and wet H-2. A substantial increase in the thickness of the oxide layers formed by the interconnect steel is observed with specimen containing talc. The Cr2O3/(Cr, Mn)(3)O-4 duplex layer normally formed on the Crofer is replaced by a thicker (factor of 5-10) layer of a complex microstructure that is assumed to contain Cr2O3, (Cr, Mn, Mg, Fe)(3)O-4 and Fe2O3 phases. The modified microstructure is found in the entire air manifold, with an increased thickness up to a distance of 300 mu m from the mica. It is proposed that magnesium is the critical component responsible for the accelerated oxide formation. A decomposition of talc is observed, which is discussed as the mechanism for the release of magnesium.