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Formula: Ce2Al(SiO4)2(OH)
Nesosilicate (insular SiO4 groups), cerium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.94 measured, 5.12 calculated
Hardness: 4½
Colour: Olive-green, brown
Solubility: Slowly dissolved by hot, concentrated hydrochloric acid
Environments
Carbonatites
Metamorphic environments
Localities
The Biraya Fe-REE ore occurrence, Biraya and Bya Rivers confluence area, Vitim Plateau, Irkutsk Oblast, Russia,
comprises a sequence of lens-shaped carbonatite bodies
accompanied by fenites, which are between 50 and 300 m in thickness and
up to 10 km long. Cordylite-(La) was discovered in a fine- to medium-
grained vein composed mainly of the carbonates
aragonite–strontianite,
emmonite, strontium-rich
calcite, iron-bearing
dolomite, cordylite-(La) and
cordylite-(Ce).
Minerals in the outer zone of the vein near the fenite include
tremolite, winchite,
ferriallanite-(Ce), törnebohmite-(Ce),
belkovite, ancylite-(La),
strontianite,
fergusonite-(Ce), zero-valent-dominant
light rare earth element-bearing
pyrochlore,
niobo-aeschynite-(Ce) and
niobo-aeschynite-(Nd)
(CM 50.1281-1290).
Törnebohmite-(Ce) from the Biraya
Fe-REE ore occurrence - Image
At the type locality, the Bastnäs Mines, Riddarhyttan, Skinnskatteberg, Västmanland County, Sweden,
törnebohmite-(Ce) belongs to the cerite-(CeCa) –
ferriallanite-(Ce) association (the major REE ore) in the
contact metamorphosed
limestone deposit. The mineral grains are anhedral, typically slightly
elongate, and 0.05 to 1 mm in length. Crystal aggregates of törnebohmite-(Ce) may exceptionally reach 5 mm
across. The mineral is most closely associated with
ferriallanite-(Ce), with which it commonly is in direct contact or
occasionally intergrown. In a few cases, lamellae of törnebohmite-(Ce), ~20 mm or wider, have been found
regularly arranged in a host crystal of ferriallanite-(Ce). In a
similar fashion, törnebohmite-(Ce) may contain oriented lamellae of
ferriallanite-(Ce), although irregular inclusions of this mineral
are more common. Törnebohmite-(Ce) locally occurs without any particular spatial relation to
ferriallanite-(Ce); it is then surrounded by
cerite-(CeCa). At rare contacts with patches of
bastnäsite, the crystals tend to be subhedral
(CM 45.5.1073-1114).
Törnebohmite-(Ce) from the Bastnäs Mines -
Image
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