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

Plutonic igneous environments
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).


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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