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Formula: Na2AlSi3O8(OH)
Tectosilicate (framework silicate)
Specific gravity: 2.48
Hardness: 6 to 7
Streak: White
Colour: Pale to medium violet, reddish violet, sometimes barely tinted purple
Solubility: Easily fusible, gelatinises with acids (Dana)
Common impurities: Ca,K,Cl,H2O,S
Environments:
Plutonic igneous environments
Pegmatites
Ussingite occurs in syenite
pegmatites and and associated
sodalite xenoliths
(Webmin, Dana).
Localities
At Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, ussingite occurs in
sodalite xenoliths in an intrusive alkalic
gabbro - syenite complex,
associated
with villiaumite, lovozerite,
eudialyte, lueshite,
griceite and natrophosphate
(HOM).
At the type locality, the Kangerluarsuk Fjord, Ilímaussaq complex, Narsaq, Kujalleq, Greenland, ussingite occurs
as a
secondary mineral in a
syenite
pegmatite, and in
sodalite-bearing xenoliths (Mindat). Associated minerals include
microcline, natrolite and
aegirine
(HOM).
At the Palitra pegmatite, Karnasurt mine, Kedykverpakhk Mountain, Lovozersky District, Murmansk Oblast, Russia,
ussingite occurs as masses to 10 cm closely associated with sodalite,
steenstrupine-(Ce),
lomonosovite,
vuonnemite and serandite.
Ussingite
replaces analcime, and
pseudomorphs of
ussingite after analcime are common
(Minrec 36.5.412).
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