This specification covers special aggregates for use in radiation-shielding concretes in which composition or high specific gravity, or both, are of prime consideration. Aggregates covered by specification include the natural mineral aggregates of either high density or high fixed water content, or both. These include aggregates that contain or consist predominately of materials such as barite, magnetite, hematite, ilmenite, and serpentine. Also included are synthetic aggregates such as iron, steel, ferrophosphorus and boron frit or other boron compounds. Fine aggregate consisting of natural or manufactured sand including high-density minerals. Coarse aggregate may consist of crushed ore, crushed stone, or synthetic products, or combinations or mixture thereof. Aggregates shall meet the required uniformity of specific gravity and fixed water content. The materials shall also meet the required chemical composition for serpentine, limonite, goethite, barite, ilmenite, hematite, magnetite, iron, ferrophosphorus, boron frit, boron carbide, calcium carbide.