During World War I, France had been using German Spark plugs in their vehicles and then were confronted with the necessity of making their own. A chemist, Mr. Delaunay, was assigned the task of developing a material which turned out to be 'ISOLANTITE' which has since become almost a trade name.
Mr. Delaunays brother-in law, Mr. Richieu, a sergeant, went into no-mans land and brought back Major De Caplane, who as a reward, offered to supply Mr. Richieu with all the money he needed for a business after the war. The outcome was that Isolantite Co., Inc. of America started in 1920 for the purpose of making spark plugs, but these turned out to be not as good as the American 'Andalucite plugs', developed in the Bureau of Standards, however, in the early 1920s, it was discovered that Isolantite was ideal material for radio frequency applications. Hence, Isolantite was used by General Electric, Radio Corporation of America and Westinghouse and others for their communication insulator problems. These same customers, still use it.
Technical - from wikipedia
Soapstone (also known as steatite or soaprock) is a talc-schist, which is a type of metamorphic rock. It is composed largely of the magnesium rich mineral talc. It is produced by dynamothermal metamorphism and metasomatism, which occur in the zones where tectonic plates are subducted, changing rocks by heat and pressure, with influx of fluids, but without melting. It has been a medium for carving for thousands of years.
Steatite ceramics are low-cost biaxial porcelains of nominal composition (MgO)3(SiO2)4. Steatite is used primarily for its dielectric and thermal insulating properties in applications such as tile, substrates, washers, bushings, beads, and pigments. It is also used for high-voltage insulators, which have to stand large mechanical loads, e.g. insulators of mast radiators.