Mayenite supergroup, part I: Recommended nomenclature
Galuskin, Evgeny V.; Gfeller, Frank; Galuskina, Irina O.; Armbruster, Thomas; Bailau, Radu; Sharygin, Viktor V.
published: Feb 1, 2015
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 Å) with the general formula X 12 T 14O32–x(OH)3x[W 6–3x]: 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 X 12 T 14O32[W 6] 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)4F2]. 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.