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Formula: NaNa2(Fe2+4Fe3+)Si8O22(OH)2
Inosilicate (chain silicate),
arfvedsonite root name group,
amphibole
Crystal System: Monoclinic
Specific gravity: 3.3 to 3.5 measured, 3.33 calculated
Hardness: 5 to 6
Streak: Pale to dark blue-grey
Colour: Bluish-black to black
Common impurities: Ti,Mn,Ca,Al,K,F
Environments:
Plutonic igneous environments
Pegmatites
Metamorphic environments
Arfvedsonite is common in alkalic granite and other plutonic
rocks
and pegmatites, associated with
nepheline, albite,
augite, aegirine,
riebeckite, katophorite,
and
quartz.
(HOM, Dana).
It occurs both in quartz-bearing
syenite and in
nepheline syenite, generally forming late in their
crystallisation
(Dana).
Arfvedsonite is sometimes an overgrowth on earlier formed
hastingsite,
and it also occurs in soda-rich
metamorphic environments with jadeite
(Dana).
Localities
At Buchans, Newfoundland, Newfoundland and Labrador, Canada, arfvedsonite has been recognised in
prehnite-pumpellyite facies metamorphosed
basalts. It occurs sporadically within submarine vesicular
basalt dykes cutting vesicular
basaltic andesite
breccias in drillcore 800 feet beneath the polymetallic massive
sulphide deposit.
The arfvedsonite forms sharply bounded crystals and crystal fragments up to 0.15 mm long, occasionally in
contact with primary
titanium-bearing
augite and plagioclase.
Isolated grains occur within patches of secondary matrix or
amygdular (A texture in lava in which the vesicules have been mostly filled with
chalcedony or other minerals)
chlorite
(AM 63.413-414).
At Mont Saint-Hilaire, Quebec, Canada, arfvedsonite occurs in the
pegmatite
(Dana ).
The type locality is the Kangerluarsuk Fjord, Ilímaussaq complex, Greenland, Denmark.
At the Palitra pegmatite, Kola peninsula, Russia,
arfvedsonite is typical of the
eudialyte-aegirine-microcline
zone
(MinRec 36.5.402).
At Cripple Creek, Teller county, Colorado, USA, arfvedsonite occurs in
phonolite
(MinRec 36.2.163).
At Hurricane mountain, Carroll county, New Hampshire, USA, fluorine-rich arfvedsonite occurs in the
pegmatite
(Dana).
At the Buck Hill syenite Intrusion, Augusta county, Virginia, USA,
zirconium-enriched arfvedsonite is associated with
analcime
(R&M 84.4.354-355).
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