The recently reported presence of [sodium] nitrate (and alkaline earth nitrates) in lignite and in the low-temperature ash produced by oxidizing lignite in a microwave-excited plasma of atomic oxygen has elicited inquiries to the Bureau of Mines regarding such occurrence and the feasibility of recovering the nitrates. The nature of the mineral content of lignite has always been in some degree a concern of the Bureau, and more particularly in the past 8 years in relation to boiler-fouling problems. Even more recently, the mineralizing study has been extended to include coals of the western United States other than lignites. A very extensive survey of mineral matter is an on-going Bureau project which contributes to studies of fouling characteristics and of beneficiation of the coal. This article presents the recent work being done on the mineralization of coal at the Bureau of Mines laboratory in Grand Forks, North Dakota.