Formula: Ce(CO3)F
Bastnäsite-(Ce) is the most common member of the bastnäsite group
Anhydrous carbonate containing halogen, cerium-bearing mineral, may be found as pseudomorphs after fluocerite or chevkinite, and forms oriented overgrowths on fluocerite, with crystal axes of both species oriented in parallel position (Mindat)
Crystal System: Hexagonal
Specific gravity: 4.9 to 5.2 measured, 5.12 calculated
Hardness: 4 to 5
Streak: White
Colour: Yellow, reddish-brown; colourless to light yellow in transmitted light
Solubility: Soluble in strong, hot acids

Metamorphic environments
Hydrothermal environments

Bastnäsite is most commonly found in metamorphic rocks and pegmatites, associated with allanite, cerite-(CeCa), fluocerite, fluorite and tornebohmite (Mindat).
Bastnäsite-(Ce) is typically hydrothermal, although primary igneous occurrences are known, in granite and alkali syenite and pegmatites in carbonatites, in contact metamorphic deposits and rarely as a detrital mineral in placers. Associated minerals include allanite-(Ce), cerianite-(Ce), synchysite-(Ce), parisite-(Ce), cerite-(CeCa), fluocerite-(Ce) and fluorite (HOM).


At Tvedalen, Larvik, Vestfold, Norway, crystals of bastnäsite-(Ce) 10 to 20 mm in size are found in syenite pegmatites in both Tuften and Bjørndalen larvikite quarries. Aggregates and rosettes of tiny platy crystals are also observed in Heia larvikite quarry. In a syenite pegmatite dyke in Treschow quarry well developed bastnäsite-(Ce) crystals have been found lining small vugs in analcime. These vugs are actually negative crystals of a primary, probably gadolinite group, mineral. This gadolinite mineral is the precursor of bastnäsite-(Ce) which is sometimes intergrown with parisite-(Ce) (JWW p156).

The type locality for bastnäsite-(Ce) is the Bastnäs Mines, Riddarhyttan, Skinnskatteberg, Västmanland County, Sweden. Here bastnäsite-(Ce) occurs in narrow bands in a contact metamorphic amphibole skarn, associated with fluocerite, fluorite, cerite-(CeCa), allanite-(Ce) and törnebohmite. The skarn is composed largely of amphiboles, that run parallel and adjacent to the hematite ore belt, in the granulite formation, consisting of granulite, mica schist and limestone - dolostone layers (Mindat, AM 30.609-612).

At Jamestown, Jamestown Mining District, Boulder county, Colorado, USA, centimetre to decimetre sized mineralised pods and veins consist of zoned mineral assemblages dominated by fluorbritholite-(Ce) in a core 10 cm thick, with monazite-(Ce), fluorite and minor quartz, uraninite and sulphides. The core is surrounded by a typically millimetre thick rim of allanite-(Ce), with minor monazite-(Ce) in the inner part of the rim. Bastnäsite-(Ce), törnebohmite-(Ce) and cerite-(CeCa) appear in an intermediate zone between core and rim, often just a few hundreds of microns wide (R&M 96.3.252-253).

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