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Formula: (Na☐)Nb2Na3Ti(Si2O7)2O2(OH)2(H2O)4
Sorosilicate (Si2O7 groups),
lamprophyllite group,
niobium- and titanium- bearing mineral
Crystal System: Triclinic
Specific gravity: 2.65 to 2.89 measured, 2.987 calculated
Hardness: 2½ to 3
Streak: White
Colour: White, yellowish grey, pinkish beige, tan, silver on {001}
Common impurities: Al,Ta,Fe,Mn,Mg,Ca,K,F,P
Environments
Plutonic igneous environments
Pegmatites
Hydrothermal environments
Epistolite is a low temperature mineral in alkalic
pegmatites,
albitites, sodalite xenoliths
and hydrothermal veins. It is a rare mineral of nepheline syenite
massifs. Associated minerals include aegirine,
albite, murmanite,
sphalerite, manganoan
pectolite, neptunite,
steenstrupine, rinkite,
sodalite, eudialyte and
nenadkevichite
(HOM, Dana).
Epistolite alters to nenadkevichite,
gerasimovskite and other minerals
(Dana).
It forms syntactic intergrowths with murmanite
(CM 43: 973-987).
Localities
At the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, some
epistolite may be an alteration product of vuonnemite
(Dana).
At the type locality, Nunarssuatsiaq, Tunulliarfik Fjord, Ilímaussaq complex, Kujalleq, Greenland, epistolite
occurs in a nepheline syenite
pegmatite
(Dana).
It forms silvery plates associated with aegirine,
albite, murmanite,
sphalerite, neptunite,
steenstrupine-(Ce), sodalite,
eudialyte and nenadkevichite
(Mindat).
At the Malyi Punkaruaiv Mountain, Lovozersky District, Murmansk Oblast, Russia,
punkaruaivite is found within an
ussingite – aegirine –
microcline vein in
nepheline syenite, in association with
anglesite, belovite-(Ce),
chkalovite, epididymite,
epistolite, eudialyte,
ferronordite-(Ce),
karnasurtite-(Ce),
lamprophyllite,
lorenzenite,
manganoneptunite,
manganonordite-(Ce),
monazite-(Ce), murmanite,
natrolite, pectolite,
rhabdophane-(Ce),
steenstrupine-( Ce),
tainiolite, tugtupite and
vitusite-(Ce)
(CM 48.1.41–50).
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