Carbonate minerals can be separated from non-carbonate minerals by the use of 10 percent hydrochloric acid at room temperature for 24 hours. Clay minerals and pyrite are almost completely insoluble under these conditions. Gypsum, however, is soluble under the conditions used to dissolve carbonate minerals. Siderite was found to be the most difficult carbonate mineral to dissolve of the nine carbonate minerals investigated. An easily reproducible method for determing insoluble residues is proposed.