THE NOMENCLATURE OF EUDIALYTE-GROUP MINERALS

Abstract

This is the final report on the nomenclature of eudialyte-group minerals by the Eudialyte Nomenclature Subcommittee established by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. This report is an updated and slightly revised version of the one that was formally accepted by the Commission. Eudialyte-group minerals are Narich zirconosilicates with varying amounts of the cations Ca, Fe, Mn, REE, Sr, Nb, K, Y, Ti, H and W. They are trigonal, a ≈ 14 Å, c ≈ 30 Å (rarely 60 Å), crystallizing in R3̄m, R3m or R3. In order to encompass most substitutions known thus far, the general formula of eudialyte (s.l.) is [N(1)N(2)N(3)N(4)N(5)]3[M(1a)M(1b)]3M(2 3M(3)M(4)Z3[Si24O72]O' 4X2, X = Cl, F, OH or CO3; Z = 3. Lately, the number of minerals in this group has increased rapidly and is now approaching twenty. Three different principles of naming minerals have been tested: (i) a hierarchical system with root names modified by use of modifiers and Levinson suffixes. (ii) a unique-name system with use of modifiers with or without Levinson suffixes, and (iii) a system based on the Linnean principle used in the biological world. We conclude that a hierarchical nomenclature system does not work for eudialyte-group minerals. Such a system would be either a multi-level system that would become either very complicated and cumbersome, with disproportionately many root names, or a flatter system with fewer root names but monstrously long names with formula-like endings, e.g., eudialyte-NaNaNaNaNaCaMnNbSiF. Conventional unique names with a maximum of one cation prefix are recommended for the eudialyte-group minerals, and this prefix should refer to the M(2) site, as in ferrokentbrooksite. One anion prefix is acceptable as well. A Linnean system composed of a genus name with a species suffix, e.g., eudialyte khomyakovite, is evaluated. However, there is no tradition for binary names in mineralogy, and the system is not endorsed.