In this communication we present a brief response to Hawthorne (2023) who, in a paper in volume 87, doi.org/10.1180/mgm.2023.8 (this journal), claims evidence for violations of the electroneutrality principle in mineral formulae derived through IMA–CNMNC procedures: i.e. the dominant-constituent rule, the valency-imposed double site-occupancy, the dominant-valency rule, and the site-total-charge approach (STC).

His statement is not correct as the STC method is based on the end-member definition; thus, it cannot violate the requirements of an end-member, particularly the laws of conservation of electric charge. The STC was developed to address the shortcomings in the previous IMA–CNMNC procedures.

The real question is: which method to use to define an end-member formula? Currently, there are two approaches: (1) STC, which first identifies the dominant end-member charge arrangement and then leads to the dominant end-member composition; (2) the dominant end-member approach.

New guidelines for the nomenclature of polymorphs and polysomes have been approved by the the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA–CNMNC). Several cases can be distinguished. (i) Polymorphs with different crystal systems are distinguished by the prefixes cubo- (cubic), hexa- (hexagonal), tetra- (tetragonal), trigo- (trigonal), ortho- (orthorhombic), clino- (monoclinic) and anortho- (triclinic). (ii) Polymorphs with different crystal systems but showing a pseudosymmetry should show the prefix ‘pseudo-’. (iii) Polymorphs with the same crystal system but different space groups are distinguished by the prefix ‘para-’. If three or more polymorphs show the same crystal system but different space groups, the space group notation may be added as a suffix, though such a nomenclature should be avoided if possible. (iv) Polymorphs with the same space group are distinguished by the prefix ‘para-’. (v) Minerals with polymorph suffixes but with different chemical compositions cannot be considered as true polymorphs, so we recommend using the prefix ‘meta-’, which indicates a close but significantly different chemical composition. (vi) Polysomatic symbols should be placed as a suffix, which indicates the number and types of modules that alternate in the structure, such as in the högbomite supergroup, or as prefixes as in the sartorite homologous series. These recommendations have to be applied for future new mineral proposals, when the authors decide to use structural prefixes or suffixes, however modifications of historical and well-established names have to pass through the CNMNC for approval. In order to be consistent with the new guidelines, 25 mineral names are now modified: domeykite-β becomes trigodomeykite; fergusonite-(Y)-β becomes clinofergusonite-(Y); fergusonite-(Ce)-β becomes clinofergusonite-(Ce); fergusonite-(Nd)-β becomes clinofergusonite-(Nd); ice-VII becomes cubo-ice; roselite-β becomes anorthoroselite; sulphur-β becomes clinosulphur; mertieite-II becomes mertieite; mertieite-I becomes pseudomertieite; uranophane-α becomes uranophane; uranophane-β becomes parauranophane; gersdorffite-P213 becomes gersdorffite; gersdorffite-Pa3 becomes paragersdorffite; gersdorffite-Pca21 becomes orthogersdorffite; betalomonosovite becomes paralomonosovite; lammerite-β becomes paralammerite; nováčekite-I becomes hydronováčekite; nováčekite-II becomes nováčekite; halloysite-7Å becomes halloysite; halloysite-10Å becomes hydrohalloysite; metauranocircite-I becomes metauranocircite; taimyrite-I becomes taimyrite; uranocircite-II becomes uranocircite; andorite IV becomes quatrandorite; and andorite VI becomes senandorite.

The columbite supergroup is established. It includes five mineral groups (ixiolite, wolframite, samarskite, columbite and wodginite) and one ungrouped species (lithiotantite). The criteria for a mineral to belong to the columbite supergroup are: the general stoichiometry MO2; the crystal structure based on the hexagonal close packing (hcp) of anions (or close to it); the six-fold coordination number of M-type cations (augmented to eight-fold in the case of slight distortion of hcp); and the presence of zig-zag chains of edge-sharing M-centred polyhedra. The ixiolite-type structure is considered as an aristotype with the space group Pbcn, the smallest unit cell volume, and the basic vectors a0, b0 and c0. Based on the multiplying of the ixiolite-type unit cell the following derivatives are distinguished: ixiolite type [ixiolite-group minerals; a = a0, b = b0 and c = c0; space group Pbcn; the members are ixiolite-(Mn2+), ixiolite-(Fe2+), scrutinyite, seifertite and srilankite]; wolframite type [wolframite-group minerals, ordered analogues of the ixiolite type with a = a0, b = b0 and c = c0; P2/c; the members are ferberite, hübnerite, huanzalaite, sanmartinite, heftetjernite, nioboheftetjernite, rossovskyite and riesite]; samarskite type [samarskite-group minerals; a = 2a0, b = b0 and c = c0; P2/c; the members are samarskite-(Y), ekebergite and shakhdaraite-(Y)]; columbite type [columbite-group minerals; a = 3a0, b = b0 and c = c0; Pbcn; the members are columbite-(Fe), columbite-(Mn), columbite-(Mg), tantalite-(Fe), tantalite-(Mn), tantalite-(Mg), fersmite, euxenite-(Y), tanteuxenite-(Y) and uranopolycrase]; and wodginite type [wodginite-group minerals; a = 2a0, b = 2b0 and c = c0; C2/c; the members are wodginite, ferrowodginite, titanowodginite, ferrotitanowodginite, tantalowodginite, lithiowodginite and achalaite]. Samarskite-(Yb), ishikawaite and calciosamarskite are insufficiently studied, tentatively considered as possible members of the samarskite supergroup. Qitianlingite, yttrocolumbite-(Y), yttrotantalite-(Y) and yttrocrasite-(Y) are questionable and need further studies. Polycrase-(Y) is discredited as identical to euxenite-(Y). Ixiolite has been renamed as ixiolite-(Mn2+), with the end-member formula (Ta2/3Mn2+1/3)O2. Ta- and Nb-dominant analogues of ixiolite with different schemes of charge balancing have the end-member formulae (M15+0.5M23+0.5)O2, M15+2/3M22+1/3)O2, M15+0.75M2+0.25)O2 or M15+0.8□0.2)O2 and the root name ‘ixiolite’ (for M1 = Ta) or ‘nioboixiolite’ (for M1 = Nb).