Mayenite supergroup, part I: Recommended nomenclature

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, I43d, a ! 12 A˚) 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 ¼ 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 Ca12Fe 3þ 10Si4O32(Cl6). Current research on minerals and synthetic compounds indicates that minerals close to the composition of ideal end-members, such as Ca12Fe 3þ 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 chlormaye- nite and is therefore discredited. By analogy with chlormayenite we changed the name of kyuygenite into chlorkyuygenite.