Arfvedsonite

{{Short description|Sodium amphibole mineral}}

{{Infobox mineral

| name = Arfvedsonite

| category = Inosilicates
Amphiboles

| image = Arfvedsonit-167989.jpg

| imagesize = 260px

| alt =

| caption =

| formula = [Na][Na₂][(Fe²⁺)₄Fe³⁺][(OH)₂|Si₈O₂₂]

|IMAsymbol=Arf{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| molweight =

| strunz = 9.DE.25 (10 ed)
VIII/F.08-100 (8 ed)

| dana = 66.1.3c.9

| system = Monoclinic

| class = Prismatic (2/m)
(same H-M symbol)

| symmetry = C2/m

| color = Black, deep green on thin edges

| colour =

| habit = Fibrous, radial prismatic aggregates

| twinning = Simple or lamellar parallel to [100]

| cleavage = Perfect on [110]

| fracture = Uneven

| tenacity = Brittle

| mohs = 5–6

| luster = Vitreous

| streak = Deep bluish gray, gray-green

| diaphaneity = Translucent to opaque

| gravity = 3.3–3.5

| density =

| polish =

| opticalprop = Biaxial (−)

| refractive = n_α = 1.652–1.699
n_β = 1.660–1.705
n_γ = 1.666–1.708

| birefringence = δ = 0.014

| pleochroism = Strong: Blue-greens, yellow-browns, gray-violets

| 2V =

| dispersion = r > v strong

| extinction =

| length fast/slow =

| fluorescence=

| absorption =

| melt =

| fusibility =

| diagnostic =

| solubility =

| other =

| alteration =

| references = [http://rruff.geo.arizona.edu/doclib/hom/arfvedsonite.pdf Arfvedsonite]. Handbook of Mineralogy[http://www.mindat.org/min-325.html Arfvedsonite]. Mindat.org[http://webmineral.com/data/Arfvedsonite.shtml Arfvedsonite]. Webmineral{{Cite web |url=http://pubsites.uws.edu.au/ima-cnmnc/ |title=IMA Master List |access-date=2014-05-12 |archive-date=2015-01-05 |archive-url=https://web.archive.org/web/20150105154315/http://pubsites.uws.edu.au/ima-cnmnc/ |url-status=dead }}

}}

Arfvedsonite ({{IPAc-en|ˈ|ɑːr|v|ɛ|d|s|ə|n|aɪ|t}}{{Cite book|title=The Chambers Dictionary|publisher=Chambers|year=2003|isbn=0-550-10105-5|edition=9th|chapter=arfvedsonite}}) or soda hornblende (partiellement obsolète) 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.

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