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Carbonatites are redefined using a mineralogical-genetic classification and divided into two groups: primary carbonatites, and carbothermal residua. Attention is drawn to the fact that carbonatite is both a petrographic term applicable to a particular rocktype as well as a group name applied to a complex of related carbonate and silicate rocks in a magmatic or extrusive complex. Primary carbonatites, in terms of mineralogical-genetic classifications, rather than simple modal classifications, can be divided into a group of bona fide magmatic carbonatites formed from diverse mantle-derived magmas, i.e., carbonatites associated with the melilitite, nephelinite, aillikite and kimberlite clans, with the latter best being termed calcite kimberlites. Each magma type and associated carbonatites are considered to be genetically distinct, and formed at different depths in the upper mantle by different degrees of partial melting. Carbonatites associated with the melilitite and nephelinite clans can have a multiplicity of origins, and may be formed by fractional melting, fractional crystallization or liquid immiscibility. Calcite kimberlites are smallvolume late-forming differentiates that are not related to other carbonatites or their parental magmas. The origin and genetic relationships of the Oldoinyo Lengai natrocarbonatite cannot be unambiguously determined, although these rocks are regarded as a distinct variety of primary carbonatite. Carbonate-rich rocks associated with diverse potassic or sodic peralkaline saturated to undersaturated magmas derived predominantly from metasomatized lithospheric mantle, together with REE-carbonate-rich rocks of undetermined genesis, are best termed carbothermal residua rather than carbonatite. There can be mineralogical (or modal) convergence between these rocks and low-pressure REE-rich derivatives of bona fide primary carbonatites. Carbonate-rich rocks formed by pneumatolytic reactions or anatectic melting of crustal rocks should not be considered to be carbonatites. soMMAIRe Le clan des carbonatites est ici redéfini dans le contexte d'une classification minéralogique et génétique, et subdivisé en deux groupes: carbonatites primaires et résidus carbothermaux. On souligne le fait que "carbonatite" est à la fois un terme pétrographique applicable à un type de roche particulier, et un terme faisant référence à un groupe de roches, et appliqué à des roches carbonatées and silicatées génétiquement liées dans un complexe magmatique ou extrusif. On peut diviser les carbonatites primaires, en termes de classifications minéralogiques et génétiques plutôt que de simples classifications modales, en un groupe de carbonatites véritablement magmatiques formées à partir de divers magmas mantelliques, i.e., carbonatites associées aux clans de mélilitite, néphélinite, aillikite et kimberlite, avec ces dernières manifestations préférablement appelées kimberlites à calcite. Chaque type de magma et les carbonatites associées seraient génétiquement distincts, et formées à des profondeurs différentes du ...

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On the basis of extensive studies of synthetic perovskite-structured compounds it is possible to derive a hierarchy of hettotype structures which are derivatives of the arisotypic cubic perovskite structure (ABX3), exemplified by SrTiO3 (tausonite) or KMgF3 (parascandolaite) by: (1) tilting and distortion of the BX6 octahedra; (2) ordering of A- and B-site cations; (3) formation of A-, B- or X-site vacancies. This hierarchical scheme can be applied to some naturally-occurring oxides, fluorides,hydroxides, chlorides, arsenides, intermetallic compounds and silicates which adopt such derivative crystal structures. Application of this hierarchical scheme to naturally-occurring minerals results in the recognition of a perovskite supergroup which is divided into stoichiometric and non-stoichiometricperovskite groups, with both groups further divided into single ABX3 or double A2BB'X6 perovskites. Subgroups, and potential subgroups, of stoichiometric perovskites include: (1) silicate single perovskites of the bridgmanite subgroup;(2) oxide single perovskites of the perovskite subgroup (tausonite, perovskite, loparite, lueshite, isolueshite, lakargiite, megawite); (3) oxide single perovskites of the macedonite subgroup which exhibit second order Jahn-Teller distortions (macedonite, barioperovskite); (4) fluoride singleperovskites of the neighborite subgroup (neighborite, parascandolaite); (5) chloride single perovskites of the chlorocalcite subgroup; (6) B-site cation ordered double fluoride perovskites of the cryolite subgroup (cryolite, elpasolite, simmonsite); (7) B-site cation orderedoxide double perovskites of the vapnikite subgroup [vapnikite, (?) latrappite]. Non-stoichiometric perovskites include: (1) A-site vacant double hydroxides, or hydroxide perovskites, belonging to the söhngeite, schoenfliesite and stottite subgroups; (2) Anion-deficient perovskitesof the brownmillerite subgroup (srebrodolskite, shulamitite); (3) A-site vacant quadruple perovskites (skutterudite subgroup); (4) B-site vacant single perovskites of the oskarssonite subgroup [oskarssonite]; (5) B-site vacant inverse single perovskites of the coheniteand auricupride subgroups; (6) B-site vacant double perovskites of the diaboleite subgroup; (7) anion-deficient partly-inverse B-site quadruple perovskites of the hematophanite subgroup.