Arfvedsonite
Current inventory:  0 gems
 

  
Arfvedsonite is named after the Swedish chemist, Johan A. Arfvedson (1792-1841).

Discovered in 1823;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

NaNa₂[(Fe²⁺,Mg)₄Fe³⁺]Si₈O₂₂(OH)₂

Sodium Iron Magnesium Silicate Hydroxide

Molecular Weight:

958.89 gm

Composition:

Sodium

7.19 %

Na

9.70 %

Na₂O

Iron

29.12 %

Fe

29.97 %

FeO / 8.33 % Fe₂O₃

Silicon

23.43 %

Si

50.13 %

SiO₂

Hydrogen

0.21 %

H

1.88 %

H₂O

Oxygen

40.04 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/F.08-100

Nickel-Strunz 10th Ed. ID:

9.DE.25

9 : SILICATES (Germanates)
D : Inosilicates
E : Inosilicates with 2-periodic double chains, Si₄O₁₁; Clinoamphiboles

Related to:

Amphibole Group, Sodic Clino-Amphibole Subgroup. Arfvedsonite-Magnesio-Arfvedsonite Series.

Members of Group:

Amphibole Group: Mg-Mn-Fe-Li Clino-Amphibole Subgroup, Calcic Clino-Amphibole Subgroup, Sodic Clino-Amphibole Subgroup, Mg-Fe-Mn-Li Ortho-Amphibole Subgroup

Varieties:

Anophorite, Juddite

Synonyms:

Arfvedsonite (of Brooke), Arfwedsonite, Soda-Hornblende

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Commonly as elongated prisms, striated and unterminated, to 0.60 m; may be tabular. As prismatic aggregates and radiating fibrous clusters.

Twinning:

Simple or lamellar twinning

Physical Properties

Cleavage:

Perfect on {110}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

3.44 - 3.45 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Black, Bluish Gray, deep Green on thin edges

Transparency:

Transparent to Opaque

Luster:

Vitreous (glassy); Silky when fibrous

Refractive Index:

1.652 - 1.708  Biaxial ( - )

Birefringence:

0.009 - 0.014

Dispersion:

Strong; r > v

Pleochroism:

Strong, in blue-greens, yellow-browns, or gray-violets.

Occurances

Geological Setting:

Common in alkalic granites and other alkalic plutonic rocks and pegmatites.

Common Associations:

Nepheline, Albite, Aegirine, Riebeckite, Katophorite, Magnesio-katophorite, Quartz.

Common Impurities:

Ti, Mn, Ca, Al, K, F

Type Locality:

Kangerdluarssuq (Kangerdluarsuk) Firth, Ilimaussaq complex, Narsaq, Kitaa (West Greenland) Province, Greenland

Year Discovered:

1823

View mineral photos:

Arfvedsonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Arfvedsonite is a sodium rich Amphibole Group mineral whose members are important rock forming minerals. It is an uncommon mineral and gem. Arfvedsonite is mostly glassy black but can show beautiful chatoyancy with flashes of blue, green and gold. It is almost always opaque, except in thin slices, so cabochons are the most common gem form.

The best localities for finding Arfvedsonite include Mont Saint-Hilaire, Quebec, Canada; the Ilimaussaq Intrusion, in Southern Greenland; the agpaitic pegmatites of the Kola Peninsula, Russia and Langesundfjord, Norway.
 

  
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