‖ fettsteinMin.|ˈfɛtstaɪn| [Ger.fettstein (Werner 1808), f.fett fat + stein stone.] = elæolite. 1815W. Phillips Outl.Min.Geol. (1818) 32 The fettstein consists of 44 silex, 34 alumine, 4 oxide of iron, a small portion of lime, and 16 parts of soda and potash.1859Page Geol. Termss.v.