The term mineral matter refers to the inorganic constituents of coal and is all of the elements that are not part of the organic coal substance (carbon, hydrogen , nitrogen , oxygen , and sulfur). The mineral matter is the principal source of the elements that make up the ash when the coal is burned in air or oxygen. Four of the five elements generally considered to be organic (carbon, hydrogen , oxygen , and sulfur) are also present in inorganic combination in coals.

Carbon is present in mineral (usually , calcium, magnesium , and iron) carbonates; hydrogen is present in free water and in water of hydration ; oxygen is present in oxides , water , sulfates, and silicates ; and sulfur is present in sulfides and sulfates. Mineral matter in coal is usually classified as inherent mineral matter , or adventitious mineral matter. Inherent mineral matter is the inorganic material that is too closely associated with the coal substance to be readily separated from it by methods available at present. Adventitious mineral matter is the inorganic material that is less intimately associated with the coal and can readily be separated.