Manaevite-(ce)

Chemical Properties

Chemical Formula

(Ca13Ce4[H2O]2)Mg(Al3Mg)(Mg3Ti3Fe3+2)(☐4)☐[Si2O7]4[(SiO4)8(H4O4)2]O(OH)9 The formula is a partial simplification of the full structural formula. The large (VII-IX)-coordinated (X4)2(X3)8(X2)8(X1) sites are here combined (e.g. Ca19) and are typically filled with Ca, although other large cations such as the REE may be present. The square-pyramidal Y1 site can host a variety of M2+ and M3+ ions and is the basis for the distinction of several species. The VI-coordinated Y2 site typically is filled with Al, whereas the also VI-coordinated Y3 site may contain Al, Mg, and other cations of similar charge and size. The tetrahedral T1 site is typically vacant but may contain B (less commonly Al); the trigonal T2 site is also typically vacant but may also contain B. Some of the (SiO4) may be replaced by (H4O4), akin to the Si4+ ↔︎ 4H+ hydrogarnet substitution. Among the oxygen that are not part of the silica tetrahedra, there are eight "O11" that typically occur as OH, two "O10" that are typically O & OH or OH & OH (the latter arrangement notably when Y1 is an M2+ cation). There may also be up to three "O12" that in most vesuvianite-group minerals are absent (and are not included here), but may be present particularly when T1 is occupied. Note that in lieu of published structural data, the Y2 and Y3 site occupancies denoted here are distributed as per other members of the other vesuvianite group minerals (i.e. Y2 = Al-dominant; Ti & Fe3+ assigned to Y3). These occupancies may be re-assigned with updated data. Justification for the -(REE) suffix is that REE (in this case predominately Ce) is the dominant cation in the X3 site.

Elements

Al, Ca, Ce, Fe, H, Mg, O, Si, Ti