The term 'Limestone Source' can be summarized by the crossword solution 'QUARRY, ' which is a type of open-pit mine from which rocks or minerals are extracted. Quarries are typically used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. Limestone is a sedimentary rock composed mostly of calcium carbonate, and quarries are often used to extract this material for use in construction and other industries.