Fengchengite

Fengchengite is a rare mineral of the eudialyte group^[2] with the formula Na₁₂[ ]₃(Ca,Sr)₆Fe₃³⁺Zr₃Si(Si₂₅O₇₃)(H₂O,OH)₃(OH,Cl)₂.^[3][2] The formula is simplified as it does not show the presence of cyclic silicate groups. When compared to other minerals of the group, fengchengite characterizes in the presence of ferric iron (thus similar to ikranite, mogovidite and feklichevite^[2]) and essential, site-dominating vacancies. The mineral was discovered in the Saima complex near Fengcheng city in China – hence its name.^[2][3]

Fengchengite
General
Category	Cyclosilicate
Formula	Na12[ ]3(Ca,Sr)6Fe33+Zr3Si(Si25O73)(H2O,OH)3(OH,Cl)2
IMA symbol	Fcg[1]
Crystal system	Trigonal
Crystal class	Hexagonal scalenohedral (3m) H-M symbol: (3 2m)
Space group	R3m
Unit cell	a = 14.25, c = 30.03 [Å] (approximated)
Identification
References	[2][3]