Afghanite

{{Short description|Tectosilicate mineral in the feldspathoid group}} {{Infobox mineral | name = Afghanite | image = Afghanite (Afghanistan) 1.jpg | imagesize = 260 | alt = | caption = Afghanite (light blue) with sodalite/lazurite (blue) coating | category = Tectosilicate minerals | group = Feldspathoid group, cancrinite group | formula = (Na,K)₂₂Ca₁₀[Si₂₄Al₂₄O₉₆](SO₄)₆Cl₆ |IMAsymbol=Afg<ref>{{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}}</ref> | strunz = 9.FB.05 | dana = | system = Trigonal | class = Ditrigonal pyramidal <br/>H-M symbol: (3m) | symmetry = ''P3c1''<ref name="Ballirano et al. 1997">{{Cite journal|url=https://www.schweizerbart.de/papers/ejm/detail/9/83316/Crystal_structure_of_afghanite_the_eight_layer_member_of_the_cancrinite_group_evidence_for_long_range_Si_Al_ordering|doi=10.1127/ejm/9/1/0021|title=Crystal structure of afghanite, the eight-layer member of the cancrinite-group: Evidence for long-range Si,Al ordering|year=1996|last1=Ballirano|first1=Paolo|last2=Bonaccorsi|first2=Elena|last3=Maras|first3=Adriana|last4=Merlino|first4=Stefanο|journal=European Journal of Mineralogy|volume=9|issue=1|pages=21–30|bibcode=1996EJMin...9...21B|url-access=subscription}}</ref> | unit cell = a = 12.796, c = 21.409&nbsp;[Å]; Z&nbsp;=&nbsp;1 | color = light blue, dark blue | colour = | habit = elongated, bullet-like crystals with pointed ends | twinning = | cleavage = Perfect {10{{overline|1}}0} | fracture = Conchoidal | tenacity = | mohs = 5.5–6 | luster = Vitreous | streak = white | diaphaneity = Transparent | gravity = 2.55–2.65 | density = | polish = | opticalprop = Uniaxial (+) | refractive = n_ω = 1.523 n_ε = 1.529 | birefringence = δ = 0.006 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other =25px Radioactive 2.28% (K) | references = <ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/afghanite.pdf Mineral Data Publishing 2001]</ref><ref name=Mindat>[http://www.mindat.org/min-41.html Mindat with location data]</ref><ref name=Webmin>[http://www.webmineral.com/data/Afghanite.shtml Webmineral data]</ref><ref>{{Cite web|url=http://www.classicgems.net/info_Radioactive.htm|title = Radioactive Gems : ClassicGems.net}}</ref> }} '''Afghanite''', (Na,K)₂₂Ca₁₀[Si₂₄Al₂₄O₉₆](SO₄)₆Cl₆,<ref name="Ballirano et al. 1997"/> is a hydrous sodium, calcium, potassium, sulfate, chloride, carbonate alumino-silicate mineral. Afghanite is a feldspathoid of the cancrinite group and typically occurs with sodalite group minerals. It forms blue to colorless, typically massive crystals in the trigonal crystal system. The lowering of the symmetry from typical (for cancrinite group) hexagonal one is due to ordering of Si and Al.<ref name="Ballirano et al. 1997"/> It has a Mohs hardness of 5.5 to 6 and a specific gravity of 2.55 to 2.65. It has refractive index values of nω = 1.523 and nε = 1.529. It has one direction of perfect cleavage and exhibits conchoidal fracture.<ref name=Mindat/> It fluoresces a bright orange. thumb|left|Afghanite (light blue) with lazurite (blue) coating

It was discovered in 1968 in the Lapis-lazuli Mine, Sar-i Sang, Badakhshan Province, Afghanistan and takes its name from that country. It has also been described from localities in Germany, Italy, the Pamir Mountains of Tajikistan, near Lake Baikal in Siberia, New York and Newfoundland. It occurs as veinlets in lazurite crystals in the Afghan location and in altered limestone xenoliths within pumice in Pitigliano, Tuscany, Italy.<ref name=HBM/>

It is used as a gemstone.<ref>Tables of Gemstone Identification, By Roger Dedeyne, Ivo Quintens, p.112</ref> {{clear left}}

==See also== * List of gemstones * List of minerals

==References== {{Reflist}}

{{Commons category}}

Category:Sodium minerals Category:Potassium minerals Category:Calcium minerals Category:Aluminium minerals Category:Trigonal minerals Category:Minerals in space group 159 Category:Gemstones Category:Minerals described in 1968 Category:Cancrinite group