I Had a friend Once

Who asked me if me or my chemistry inclined friend knew of a heavy gas and a light solid substance existed such that the solid would float in the gas at anything like normal temperature and pressure. My instinct told me something like Uranium Hexafluoride and a light metal like lithium may work (of course, it might explode) at a temperature and pressure higher than room and atmospheric. I also thought some solid like pumice would also work, but may be disqualified due to its high gas content.