A composite seal is disclosed having first and second metal layers overlying one another in spaced relation. A mineral layer is positioned between the metal layers. The metal and mineral layers have inner and outer perimeters, the inner perimeters overlapping to define an aperture. The metal layers are joined at a perimeter, preferably the outer perimeter, by welding. The metal layers are preferably precious metal or high temperature alloy foil and the mineral layer may be formed of mica, vermiculite, or modifications of vermiculite.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made at least in part with funding from the United States Department of Energy under DOE Cooperative Agreement No. DE-FC26-98FT40343. The United States Government has certain rights in this invention.