Arfvedsonite

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.

Arfvedsonite
General
CategoryInosilicates
Amphiboles
Formula
(repeating unit)		[Na][Na2][(Fe2+)4Fe3+][(OH)2|Si8O22]
Strunz classification9.DE.25 (10 ed)
VIII/F.08-100 (8 ed)
Dana classification66.1.3c.9
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Identification
ColorBlack, deep green on thin edges
Crystal habitFibrous, radial prismatic aggregates
TwinningSimple or lamellar parallel to [100]
CleavagePerfect on [110]
FractureUneven
TenacityBrittle
Mohs scale hardness5–6
LusterVitreous
StreakDeep bluish gray, gray-green
DiaphaneityTranslucent to opaque
Specific gravity3.3–3.5
Optical propertiesBiaxial (-)
Refractive indexnα = 1.652–1.699
nβ = 1.660–1.705
nγ = 1.666–1.708
Birefringenceδ = 0.014
PleochroismStrong: Blue-greens, yellow-browns, gray-violets
Dispersionr > v strong
References[1][2][3][4]

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

References
  1. Arfvedsonite. Handbook of Mineralogy
  2. Arfvedsonite. Mindat.org
  3. 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
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