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Arfvedsonite from New Hampshire, USA
Category Inosilicates
(repeating unit)
Strunz classification 9.DE.25 (10 ed)
VIII/F.08-100 (8 ed)
Dana classification 66.1.3c.9
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/m
Color Black, deep green on thin edges
Crystal habit Fibrous, radial prismatic aggregates
Twinning Simple or lamellar parallel to [100]
Cleavage Perfect on [110]
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 5–6
Luster Vitreous
Streak Deep bluish gray, gray-green
Diaphaneity Translucent to opaque
Specific gravity 3.3–3.5
Optical properties Biaxial (-)
Refractive index nα = 1.652–1.699
nβ = 1.660–1.705
nγ = 1.666–1.708
Birefringence δ = 0.014
Pleochroism Strong: Blue-greens, yellow-browns, gray-violets
Dispersion r > v strong
References [1][2][3][4]

Arfvedsonite is a sodium amphibole mineral with composition: [Na][Na2][(Fe2+)4Fe3+][(OH)2|Si8O22]. It crystallizes in the monoclinic prismatic crystal system and typically occurs as greenish black to bluish grey fibrous to radiating or stellate prisms.

It is a rather rare mineral occurring in nepheline syenite intrusions and agpaitic (peralkaline) pegmatites and granites as the Golden Horn batholith in Okanogan County, Washington (type locality for zektzerite). Occurrences include Mont Saint-Hilaire, Quebec, Canada; the Ilímaussaq complex in Southern Greenland; and in pegmatites of the Kola Peninsula, Russia. Its mineral association includes nepheline, albite, aegirine, riebeckite, katophorite and quartz.[1]

Arfvedsonite was discovered in 1823 and named for the Swedish chemist Johan August Arfwedson (1792–1841).[3]

See also[edit]

Arfvedsonite, Poudrette quarry, Mont Saint-Hilaire, Montérégie, Quebec


  1. ^ a b Arfvedsonite. Handbook of Mineralogy
  2. ^ Arfvedsonite.
  3. ^ a b Arfvedsonite. Webmineral
  4. ^ IMA Master List
  • Deer, W.A., R.A. Howie, and J. Zussman (1963) Rock-forming Minerals, v. 2, Chain Silicates, p. 364–374
  • Mineral Galleries