Aeschynite

oxide

pegmatite

Formulae:
aeschynite-(Ce): (Ce,Ca,Fe,Th)(Ti,Nb)2(O,OH)6
aeschynite-(Nd): (Nd,Ln,Ca)(Ti,Nb)2(O,OH)6
aeschynite-(Y): (Y,Ln,Ca,Th)(Ti,Nb)2(O,OH)6 most common
Multiple oxides containing niobium, tantalum or titanium
Aeschynite-(Ce) forms series with nioboaeschynite-(Ce) and with aeschynite-(Y) (Mindat ).
Aeschynite-(Y) forms series with aeschynite-(Ce) and with tantalaeschynite-(Y) (Mindat).

Specific gravity:
aeschynite-(Ce): 5.19
aeschynite-(Nd): 4.6 to 5.04
aeschynite-(Y) 4.82 to 4.93
Hardness: aeschynite-(Ce), (Nd) and (Y) 5 to 6
Streak:
aeschynite-(Ce) Nearly black to brown
aeschynite-(Nd) Light yellowish brown
aeschynite-(Y) White, pale yellow, reddish yellow
Colour:
aeschynite-(Ce) Black, brown, light brown to yellow
aeschynite-(Nd) Dark to pale brown, brownish black
aeschynite-(Y) Pale yellow, yellow-orange, pale greenish yellow, black, brownish black
Solubility: aeschynite-(Y) is insoluble in hydrochloric acid, and soluble in HF or in a fusion with KHSO4 (Dana).
Environments

Plutonic igneous environments
Pegmatites
Carbonatites
Placer deposits
Metamorphic environments

Aeschynite-(Ce)

Aeschynite-(Ce) occurs in nepheline syenite, in granite pegmatites and in carbonatites in alkaline rocks; it is also a detrital mineral in placers. It is often metamict. Associated minerals include feldspar, zircon, samarskite, columbite, allanite and titanite (HOM, Mindat).

The type locality for aeschynite-(Ce) is the Gadolinite Pit, Chelyabinsk Oblast, Russia.

At the Dark Star claim, Ravalli county, Montana, USA, aeschynite-(Ce) occurs in carbonatite rocks associated with allanite, apatite, monazite, fersmite, magnetite, pyrite and columbite (Dana).

Common impurities in aeschynite-(Ce): REE,Sn

Aeschynite-(Nd)

At the type locality for aeschynite-(Nd), the East Mine, Bayan Obo deposit, Baotou League, Inner Mongolia, China, aeschynite-(Nd) occurs in veins in slate and metamorphosed dolostone associated with aegirine, riebeckite, baryte, fluorite, albite, phlogopite and magnetite (HOM, Mindat, AM 69.565).

Aeschynite-(Y)

Aeschynite-(Y) occurs in granite and granite pegmatites, in ankerite - dolomitic carbonatites and as a detrital mineral in placers. Associated minerals include euxenite, monazite, xenotime, allanite, zircon, fergusonite, thorite, synchysite, gadolinite, chernovite, columbite, biotite, muscovite, titanite and corundum (HOM, Mindat).

In South China aeschynite-(Y) occurs in an yttrium-rare-earth-rich muscovite granite, associated with xenotime, monazite, zircon, fergusonite, thorite, synchysite-(Y), gadolinite, chernovite, columbite and cassiterite (AM 61.178, Dana).

At the Trimouns quarry, Luzenac, Ariege, France, aeschynite-(Y) is found in the talc - chlorite mineralisation zone, filling dolomite vugs commonly associated with calcite. Some aeschynite crystals are sprinkled with limonitised pyrite (MinRec 35.3.231-232).

At the type locality for aeschynite-(Y), the Urstad Feldspar Mine, Hidra, Flekkefjord, Norway, aeschynite-(Y) occurs in a granite pegmatite.

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