The term 'USEFUL MINERAL' can be broken down into two crossword solutions: TALC (4 letters) and ORE (3 letters). TALC is a mineral composed of hydrated magnesium silicate, and is used in a variety of products such as cosmetics, paper, paint, and rubber. ORE is a rock or mineral from which a valuable metal or valuable mineral can be extracted. It is an important source of many metals, including iron, aluminum, copper, and gold.