Cerianite-(Ce)

Cerianite-(Ce) is a relatively rare oxide mineral, belonging to uraninite group with the formula (Ce,Th)O
₂.^[4][5] It is one of a few currently known minerals containing essential tetravalent cerium, the other examples being stetindite and dyrnaesite-(La).^[6][7]

Cerianite-(Ce)
Yellow powder of the very rare mineral cerianite-(Ce) from Morro do Ferro, Caldas, Minas Gerais, Brazil.
General
Category	Oxide
Formula	(Ce,Th)O 2
IMA symbol	Cei-Ce[1]
Crystal system	Isometric
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fm3m
Unit cell	a = 5.42 Å; Z = 4
Identification
Color	Dark greenish amber-yellow, yellow, buff
Crystal habit	octahedra; earthy, massive
Diaphaneity	Translucent or transparent
Density	7.20 (synth. material, calc.; approximated)
Other characteristics	Radioactive
References	[2][3][4]

Occurrence and association

Cerianite-(Ce) is associated with alkaline rocks, mostly nepheline syenites.^[3] It may be found in carbonatites.^[4] Cerianite-(Ce) associates with minerals of the apatite group, bastnäsite-group minerals, calcite, feldspar, "fluocerite", "hydromica", ilmenite, nepheline, magnetite, "törnebohmite" and tremolite.^[3] It is the most simple cerium mineral known.^[4]

Notes on chemistry

Beside thorium cerianite-(Ce) may contain trace niobium, yttrium, lanthanum, ytterbium, zirconium and tantalum.^[3]

Crystal structure

For details on crystal structure see cerium(IV) oxide. Both ceria and thoria have a fluorite structure.