Fengchengite is a rare mineral of the eudialyte group with the formula Na123(Ca, Sr)6Fe33+Zr3Si(Si24O73)(H2O, OH)3(OH, Cl)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) and essential, site-dominating vacancies.
- Category: Cyclosilicate
- Formula: Na123(Ca,Sr)6Fe33+Zr3Si(Si24O73)(H2O,OH)3(OH,Cl)2
- Crystal system Trigonal
- Crystal class: Hexagonal scalenohedral (3m)
- Member of: Eudialyte Group
- Name: Named after the nearby Fencheng city.
The mineral was discovered in the Saima complex near Fengcheng city in China – hence its name. This mineral ranks a 5 on Mohs Scale of Hardness, though it is considered brittle, exhibiting conchoidal fracture when broken.