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Formula: CaNd(Al2Fe2+)[Si2O7][SiO4]O(OH)
Sorosilicate (Si2O7 groups), allanite group of
the epidote supergroup
Crystal System: Monoclinic
Specific gravity: 3.98 measured, 4.04 calculated
Hardness: 6
Streak: Greyish brown
Colour: Dark brown to black
Common impurities: Al,Ca,Ce,Fe,La,Mg,Mn,Pr,Sm,Ti
Environments
Plutonic igneous environments
Pegmatites
Metamorphic environments
At the type locality, the Åskagen Quarry, Filipstad, Värmland, Sweden, allanite-(Nd) occurs as aggregates within
altered
thalénite-(Y). Associated minerals include
iimoriite-(Y), keiviite-(Y),
allanite-(Y) and tengerite-(Y) (AM 97.983-988).
The deposit is a pegmatite with unusually extreme light
rare-earth element enrichment and heavy rare-earth element depletion
(Mindat).
At the Kingman Feldspar Mine, Wallapai Mining District, Cerbat Mountains, Mohave County, Arizona, USA, extreme light
rare-earth element enrichment, as well as heavy rare-earth element depletion, is exemplified by the presence of
abundant large crystals of light rare-earth element-enriched allanite and a
near-absence of heavy rare-earth element-enriched minerals. Most of the
allanite is Nd-rich
allanite-(Ce). However, several of the samples have domains that are
Nd-dominant, and thus are allanite-(Nd). In the Kingman
pegmatite, allanite
occurs as large, extensively fractured pods or crude crystals up to nearly half a metre in size. The individual
crystals are nearly to completely metamict, dark brown to black in colour, euhedral to subhedral, and reach ~25 cm in
length. All of the exposed surfaces of allanite are coated with a reddish
iron oxide crust and locally with Nd-enriched bastnäsite-(Ce).
Microscopic inclusions of thorogummite occur within the
allanite
(CM 50.815-824).
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