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Sodalite

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Sodalite
General
CategoryTectosilicates without zeolitic H2O
Formula
(repeating unit)		Na
8(Al
6Si
6O
24)Cl
2
IMA symbolSdl[1]
Strunz classification9.FB.10
Crystal systemCubic
Crystal classHextetrahedral (43m)
H-M symbol:(43m)
Space groupP43n
Unit cella = 8.876(6) Å; Z = 1
Identification
ColorRich royal blue, green, yellow, violet, white veining common
Crystal habitMassive; rarely as dodecahedra
TwinningCommon on {111} forming pseudohexagonal prisms
CleavagePoor on {110}
FractureConchoidal to uneven
TenacityBrittle
Mohs scalehardness5.5–6
LusterDull vitreous to greasy
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.27–2.33
Optical propertiesIsotropic
Refractive indexn = 1.483 – 1.487
UltravioletfluorescenceBright red-orangecathodoluminescenceand fluorescence under LW and SW UV, with yellowishphosphorescence;may bephotochromicin magentas
FusibilityEasily to a colourless glass; sodium yellow flame
SolubilitySoluble inhydrochloric acidandnitric acid
References[2][3][4][5]
Major varieties
HackmaniteTenebrescent;violet-red or green fading to white

Sodalite(/ˈsoʊ.dəˌlaɪt/SOH-də-lyte) is atectosilicatemineral with the formulaNa
8(Al
6Si
6O
24)Cl
2,withroyal bluevarieties widely used as anornamentalgemstone.Although massive sodalite samples are opaque, crystals are usually transparent to translucent. Sodalite is a member of the sodalite group withhauyne,nosean,lazuriteandtugtupite.

The people of theCaral culturetraded for sodalite from theCollao altiplano.[6]First discovered by Europeans in 1811 in theIlimaussaq intrusive complexinGreenland,sodalite did not become widely important as an ornamental stone until 1891 when vast deposits of fine material were discovered inOntario,Canada.

Structure[edit]

The structure of sodalite was first studied byLinus Paulingin 1930.[7]It is a cubic mineral ofspace groupP43n (space group 218) which consists of an aluminosilicate cage network with Na+cations and chloride anions in the interframework. (There may be small amounts of other cations and anions instead.) This framework forms azeolitecage structure. Each unit cell has two cavities, which have almost the same structure as theboratecage(B
24O
48)24−
found in thezinc borateZn
4O(BO
2)
6,[8]theberyllosilicatecage(Be
12Si
12O
48)24−
,[7]and thealuminatecage(Al
24O
48)24−
inCa
8(Al
12O
24)(WO
4)
2,[9]and as in the similar mineraltugtupite(Na
4AlBeSi
4O
12Cl) (seeHaüyne#Sodalite group). There is one cavity around each chloride ion. One chloride is located at the corners of the unit cell, and the other at the centre. Each cavity haschiral tetrahedral symmetry,and the cavities around these two chloride locations are mirror images one of the other (aglide planeor a four-foldimproper rotationtakes one into the other). There are four sodium ions around each chloride ion (at one distance, and four more at a greater distance), surrounded by twelveSiO
4tetrahedra and twelveAlO
4tetrahedra. The silicon and aluminum atoms are located at the corners of atruncated octahedronwith the chloride and four sodium atoms inside.[8](A similar structure called "carbon sodalite" may occur as a very high pressure form of carbon — see illustration in reference.[10]) Each oxygen atom links between anSiO
4tetrahedronand anAlO
4tetrahedron. All the oxygen atoms are equivalent, but one half are in environments that areenantiomorphicto the environments of the other half. The silicon atoms are at the locationand symmetry-equivalent positions, and the aluminum ions at the locationand symmetry-equivalent positions. The three silicon atoms and the three aluminum atoms listed above closest to a given corner of the unit cell form a six-membered ring of tetrahedra, and the four in any face of the unit cell form a four-membered ring of tetrahedra. The six-membered rings can serve as channels in which ions can diffuse through the crystal.[11]

The structure is a crumpled form of a structure in which the three-fold axes of each tetrahedron lie in planes parallel to the faces of the unit cell, thus putting half the oxygen atoms in the faces. As the temperature is raised the sodalite structure expands and uncrumples, becoming more like this structure. In this structure the two cavities are still chiral, because noindirect isometrycentred on the cavity (i.e. a reflexion, inversion, or improper rotation) can superimpose the silicon atoms onto silicon atoms and the aluminum atoms onto aluminum atoms, while also superimposing the sodium atoms on other sodium atoms. A discontinuity of thethermal expansion coefficientoccurs at a certain temperature when chloride is replaced by sulfate or iodide, and this is thought to happen when the framework becomes fully expanded or when the cation (sodium in natural sodalite) reaches the coordinates(et cetera).[11]This adds symmetry (such as mirror planes in the faces of the unit cell) so that the space group becomes Pm3n (space group 223), and the cavities cease to be chiral and take onpyritohedral symmetry. Natural sodalite holds primarilychlorideanions in the cages, but they can be substituted by other anions such assulfate,sulfide,hydroxide,trisulfurwith other minerals in the sodalite group representing end member compositions. The sodium can be replaced by otheralkali groupelements, and the chloride by otherhalides.Many of these have been synthesized.[11]

The characteristic blue color arises mainly from cagedS−3andS4clusters.[12]

Properties[edit]

A sample of sodalite-carbonatepegmatitefrom Bolivia, with a polished rock surface.

A light, relatively hard yet fragile mineral, sodalite is named after itssodiumcontent; inmineralogyit may be classed as afeldspathoid.Well known for its blue color, sodalite may also be grey, yellow, green, or pink and is often mottled with white veins or patches. The more uniformly blue material is used injewellery,where it is fashioned intocabochonsandbeads.Lesser material is more often seen as facing or inlay in various applications.

Although somewhat similar tolazuriteandlapis lazuli,sodalite rarely containspyrite(a common inclusion in lapis) and its blue color is more like traditionalroyal bluerather thanultramarine.It is further distinguished from similar minerals by its white (rather than blue) streak. Sodalite's six directions of poor cleavage may be seen as incipient cracks running through the stone.

Most sodalite willfluoresceorange underultraviolet light,and hackmanite exhibitstenebrescence.[13]

Stereo image
Left frame
Right frame
Parallel view()
Cross-eye view()
Small specimen of sodalite from Brazil.

Hackmanite[edit]

Hackmanite dodecahedron from the Koksha Valley, Afghanistan

Hackmaniteis a variety of sodalite exhibiting tenebrescence.[14]When hackmanite from Mont Saint-Hilaire (Quebec) or Ilímaussaq (Greenland) is freshly quarried, it is generally pale to deep violet but the color fades quickly to greyish or greenish white. Conversely, hackmanite from Afghanistan and the Myanmar Republic (Burma) starts off creamy white but develops a violet to pink-red color in sunlight. If left in a dark environment for some time, the violet will fade again. Tenebrescence is accelerated by the use of longwave or, particularly, shortwaveultravioletlight.

Occurrence[edit]

Sodalite was first described in 1811 for the occurrence in itstype localityin theIlimaussaq complex,Narsaq,West Greenland.[2]

Occurring typically in massive form, sodalite is found as vein fillings in plutonicigneous rockssuch asnepheline syenites.It is associated with other minerals typical of silica-undersaturated environments, namelyleucite,cancriniteandnatrolite.Other associated minerals includenepheline,titanianandradite,aegirine,microcline,sanidine,albite,calcite,fluorite,ankeriteandbaryte.[4]

Hippo in sodalite, length 9 cm (3.5 in)

Significant deposits of fine material are restricted to but a few locales:Bancroft, Ontario(Princess Sodalite Mine), andMont-Saint-Hilaire, Quebec,in Canada; andLitchfield, Maine,andMagnet Cove, Arkansas,in the US. The Ice River complex, nearGolden, British Columbia,contains sodalite.[15]Smaller deposits are found in South America (Brazil and Bolivia), Portugal, Romania, Burma and Russia. Hackmanite is found principally in Mont-Saint-Hilaire andGreenland.

Euhedral, transparent crystals are found in northernNamibiaand in thelavasofVesuvius,Italy.

Sodalititeis a type ofextrusiveigneous rock rich in sodalite.[16]Itsintrusiveequivalent issodalitolite.[16]

History[edit]

The people of theCaralculture traded for sodalite from the Collao altiplano.[17]

Synthesis[edit]

Themesoporouscage structure of sodalite makes it useful as a container material for many anions. Some of the anions known to have been included in sodalite-structure materials includenitrate,[18]iodide,[19]iodate,[20]permanganate,[21]perchlorate,[22]andperrhenate.

See also[edit]

References[edit]

  1. ^Warr, Laurence N. (June 2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
  2. ^abMindat with locations
  3. ^Webmineral data
  4. ^abHandbook of Mineralogy
  5. ^Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed.,ISBN0-471-80580-7
  6. ^Sanz, Nuria; Arriaza, Bernardo T.; Standen, Vivien G., eds. (2015).The Chinchorro culture: a comparative perspective, the archaeology of the earliest human mummification.UNESCO Publishing. p. 162.ISBN978-92-3-100020-1.
  7. ^abLinus Pauling(1930)."The Structure of Sodalite and Helvite".Zeitschrift für Kristallographie.74(1–6): 213–225.doi:10.1524/zkri.1930.74.1.213.S2CID102105382.
  8. ^abP. Smith; S. Garcia-Blanco; L. Rivoir (1961)."A new structural type of metaborate anion".Zeitschrift für Kristallographie.115(1–6): 460–463.doi:10.1524/zkri.1961.115.16.460.S2CID93970848.
  9. ^W. Depmeier (1979)."Revised crystal data for the aluminate sodaliteCa
    8    [Al
    12    O
    24    ](WO
    4    )
    2    "    .Journal of Applied Crystallography.doi:10.1107/S0021889879013492.
  10. ^Pokropivny, Alex; Volz, Sebastian (September 2012)."'C 8 phase': Supercubane, tetrahedral, BC-8 or carbon sodalite? ".Physica Status Solidi B.249(9): 1704–1708.Bibcode:2012PSSBR.249.1704P.doi:10.1002/pssb.201248185.S2CID96089478.
  11. ^abcHassan, I.; Grundy, H. D. (1984). "The crystal structures of sodalite-group minerals".Acta Crystallographica Section B.40:6–13.doi:10.1107/S0108768184001683.
  12. ^Chukanov, Nikita V.; Sapozhnikov, Anatoly N.; Shendrik, Roman Yu.; Vigasina, Marina F.; Steudel, Ralf (23 November 2020)."Spectroscopic and Crystal-Chemical Features of Sodalite-Group Minerals from Gem Lazurite Deposits".Minerals.10(11): 1042.Bibcode:2020Mine...10.1042C.doi:10.3390/min10111042.
  13. ^Bettonville, Suzanne (25 March 2011).Rock Roles: Facts, Properties, and Lore of Gemstones.p. 98.ISBN978-1-257-03762-9.[self-published source?]
  14. ^Kondo, D.; Beaton, D. (2009)."Hackmanite/Sodalite from Myanmar and Afghanistan"(PDF).Gems and Gemology.45(1): 38–43.doi:10.5741/GEMS.45.1.38.
  15. ^Ice River deposit on Mindat
  16. ^abLe Maitre, R.W., ed. (2002).Igneous Rocks — A Classification and Glossary of Terms(2nd ed.). Cambridge: Cambridge University Press. p. 143.ISBN0-521-66215-X.
  17. ^Sanz, Nuria; Arriaza, Bernardo T.; Standen, Vivien G., eds. (2015).The Chinchorro culture: a comparative perspective, the archaeology of the earliest human mummification.UNESCO Publishing. p. 162.ISBN978-92-3-100020-1.
  18. ^Buhl, Josef-Christian; Löns, Jürgen (1996). "Synthesis and crystal structure of nitrate enclathrated sodalite Na8[AlSiO4]6(NO3)2".Journal of Alloys and Compounds.235:41–47.doi:10.1016/0925-8388(95)02148-5.
  19. ^Nakazawa, T.; Kato, H.; Okada, K.; Ueta, S.; Mihara, M. (2000). "Iodine Immobilization by Sodalite Waste Form".MRS Proceedings.663.doi:10.1557/PROC-663-51.
  20. ^Buhl, Josef-Christian (1996). "The properties of salt-filled sodalites. Part 4. Synthesis and heterogeneous reactions of iodate-enclathrated sodalite Na8[AlSiO4]6(IO3)2−x(OH·H2O)x; 0.7 < x < 1.3".Thermochimica Acta.286(2): 251–262.doi:10.1016/0040-6031(96)02971-1.
  21. ^Brenchley, Matthew E.; Weller, Mark T. (1994). "Synthesis and structures of M8[ALSiO4]6·(XO4)2, M = Na, Li, K; X = Cl, Mn Sodalites".Zeolites.14(8): 682–686.doi:10.1016/0144-2449(94)90125-2.
  22. ^Veit, Th.; Buhl, J.-Ch.; Hoffmann, W. (1991). "Hydrothermal synthesis, characterization and structure refinement of chlorate- and perchlorate-sodalite".Catalysis Today.8(4): 405–413.doi:10.1016/0920-5861(91)87019-J.

External links[edit]

Media related toSodaliteat Wikimedia Commons

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