A specimen containing ferriallanite-(Ce), as a dark brown to black layer up to 3 cm wide, in contact with greenish-white, fibrous amphibole and newly formed weathering products around the edges, from Nya Bastnäs, Sweden. Photo by Kamil Sobek. — Photo: Kamil Sobek · CC BY 4.0
Ferriallanite-(Ce)
Ferriallanite-(Ce) is an IMA-recognized mineral species in the silicate class, with the chemical formula CaCe(Fe³⁺AlFe²⁺)[Si₂O₇][SiO₄]O(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/m). It is a member of the Epidote, allanite structural group.
Key properties: Mohs hardness 6; specific gravity 4.22; Brown streak; Resinous luster; optically biaxial.
IMA symbol Faln-Ce, IMA status: approved, named in 2000.
Of metasomatic origin in alkaline granitic pegmatite.
It is found associated with Aegirine, β-fergusonite-(Y), Y-rich and normal ilvaite, hingganite-(Ce), Nd-rich allanite-(Ce), magnetite, fayalite, fluorite, zircon, quartz, kainosite-(Y).
The prefix, ferri, indicates that the mineral is the Fe3+ analog of allanite-(Ce).