The Mines and Minerals (Development and Regulation) Act, 1957, categorizes minerals into 'major' and 'minor' categories. Major minerals are those that are crucial for industrial development and national economy. Chromite, kyanite, and sillimanite are classified as major minerals due to their significant industrial applications and resource importance, particularly in steel and refractory industries. Bentonite, while important, is typically classified as a minor mineral.