Abstract

The mayenite supergroup, accepted by the IMA-CNMNC (proposal 13-C), is a new mineral supergroup comprising two groups of minerals isostructural with mayenite (space group No. 220, I4¯3d, a ≈ 12 Å) with the general formula X12T14O32−x(OH)3x[W6−3x]: the mayenite group (oxides) and the wadalite group (silicates), for which the anionic charge over 6 W sites is −2 and −6, respectively. Currently only minerals dominated by end-members with x = 0 and the simplified formula X12T14O32[W6] have been reported. The mayenite group includes four minerals: (1) chlormayenite, Ca12Al14O32[□4Cl2]; (2) chlorkyuygenite, Ca12Al14O32[(H2O)4Cl2]; (3) fluormayenite, Ca12Al14O32[□4F2]; and (4) fluorkyuygenite, Ca12Al14O32[(H2O)4 F2]. The wadalite group comprises the two mineral species wadalite, with the end-member formula Ca12Al10Si4O32[Cl6], and eltyubyuite, with the end-member formula Ca12Fe3+10Si4O32[Cl6]. Current research on minerals and synthetic compounds indicates that minerals close to the composition of ideal end-members, such as Ca12Fe3+10Si4O32[F6], Ca12Si9Mg5O32[Cl6] and Ca12Al14O30(OH)6[□6], could be found in Nature.

A detailed re-examination of the type specimens of mayenite, originally described as Ca12Al14O33, indicates that Ca12Al14O32[□4Cl2] is its correct end-member formula. Consequently, we are redefining and renaming mayenite as chlormayenite, Ca12Al14O32[□4Cl2], whereas the name mayenite would be reserved for a potential mineral with the end-member composition Ca12Al14O32[□5O]. As a consequence, the mineral brearleyite, Ca12Al14O32[□4Cl2], described in 2011 is identical with chlormayenite and is therefore discredited. By analogy with chlormayenite we changed the name of kyuygenite into chlorkyuygenite.

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