Foidolites is a fine-grained, hard rock which is a type of metasomatite, essentially altered basalt. It forms with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive rocks.
Oil Shale forms on the beds of seas and lakes and its formation starts with the organic debris settling and accumulating at the bottom of a lake or sea which are then transformed into rock with the help of high temperature and pressure.