Mayenite supergroup, part I: Recommended nomenclature

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, I$4¯$3d, a ≈ 12 Å) with the general formula X₁₂T₁₄O_32−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 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.