The criteria for the definition of a new mineral species currently used by the Commission on New Minerals Nomenclature and Classification (CNMNC) of the International Mineralogical Association are critically examined. In particular, the rule of the dominant constituent can violate the laws of conservation of electric charge. A series of additional rules: (1) valency-imposed double site-occupancy; (2) the dominant-valency rule; and (3) the site-total-charge approach, have been developed in an attempt to correct this error. However, none of these rules can overcome the fundamental flaw introduced by the rule of the dominant constituent, and the chemical formulae resulting from application of these rules can violate the requirements of an end-member, particularly that of electroneutrality. As a result, the IMA–CNMNC rules cannot derive end-member formulae for some groups of minerals, giving rise to many ad hoc decisions in defining distinct mineral species.
