1.1 This descriptive nomenclature is intended to give accurate descriptions of some common or important naturally occurring and synthetic constituents of aggregates for radiation-shielding concrete, that, at the same time, are not common or important constituents of concrete aggregates in general use. While most of the minerals and rocks discussed below may occur in small quantities in aggregates in general use, they are not major constituents of such aggregates. Common constituents of aggregates in general use are described in Descriptive Nomenclature C294. Radiationshielding concrete often contains such aggregates, but other special aggregates are used in some circumstances. 1.2 The synthetic aggregates included are ferrophosphorus and boron frit. 1.3 The descriptions are not adequate to permit the identification of materials, since accurate identification of natural and synthetic aggregate constituents in many cases can only be made by a qualified geologist, mineralogist, or petrographer, using the apparatus and procedures of those sciences. 1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.