Hongheite

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 because the Y3 site occupancy of "end-member" hongheite has not been explicitly defined, and that based on other vesuvianite-group minerals it could be likely considered as either (Fe³⁺₄Mg₄) or (Fe³⁺₆Mg₂) (with charge-balancing concomitant occupancy of the "O11" position as [OH]₉ or [(OH)₇O₂], respectively), the more generic occupancies denoted by (Fe³⁺,Mg)₈ and (OH,O)₉ have been maintained here, pending further data.

Dark green

ⓘ Bai Shanchong granite, Malage ore field, Gejiu Sn-polymetallic ore field, Gejiu City, Honghe, Yunnan, China