Formula: NaNa2(Fe2+4Fe3+)Si8O22(OH)2
Inosilicate (chain silicate), amphibole group, glaucophane subgroup
Specific gravity: 3.0 to 3.5
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 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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