Sodalite

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Sodalite
Tenebrescent
; violet-red or green fading to white

Sodalite (

tectosilicate mineral with the formula Na
8(Al
6Si
6O
24)Cl
2, with royal blue varieties widely used as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent. Sodalite is a member of the sodalite group with hauyne, nosean, lazurite and tugtupite
.

The people of the

Caral culture traded for sodalite from the Collao altiplano.[6] First discovered by Europeans in 1811 in the Ilimaussaq intrusive complex in Greenland, sodalite did not become widely important as an ornamental stone until 1891 when vast deposits of fine material were discovered in Ontario
, Canada.

Structure

The structure of sodalite was first studied by

enantiomorphic
to the environments of the other half. The silicon atoms are at the location and symmetry-equivalent positions, and the aluminum ions at the location and 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 no

thermal expansion coefficient
occurs 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).
pyritohedral symmetry
. Natural sodalite holds primarily
alkali group elements, and the chloride by other halides. Many of these have been synthesized.[11]

The characteristic blue color arises mainly from caged S−3 and S4 clusters.[12]

Properties

A sample of sodalite-carbonate pegmatite from Bolivia, with a polished rock surface.

A light, relatively hard yet fragile mineral, sodalite is named after its sodium content; in mineralogy it may be classed as a feldspathoid. 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 in jewellery, where it is fashioned into cabochons and beads. Lesser material is more often seen as facing or inlay in various applications.

Although somewhat similar to lazurite and lapis lazuli, sodalite rarely contains pyrite (a common inclusion in lapis) and its blue color is more like traditional royal blue rather than ultramarine. 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 will

tenebrescence.[13]

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

Hackmanite

Hackmanite dodecahedron from the Koksha Valley, Afghanistan

Hackmanite is 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, shortwave ultraviolet light.

Occurrence

Sodalite was first described in 1811 for the occurrence in its

West Greenland.[2]

Occurring typically in massive form, sodalite is found as vein fillings in plutonic igneous rocks such as nepheline syenites. It is associated with other minerals typical of silica-undersaturated environments, namely leucite, cancrinite and natrolite. Other associated minerals include nepheline, titanian andradite, aegirine, microcline, sanidine, albite, calcite, fluorite, ankerite and baryte.[4]

Hippo in sodalite, length 9 cm (3.5 in)

Significant deposits of fine material are restricted to but a few locales:

Mont-Saint-Hilaire, Quebec, in Canada; and Litchfield, Maine, and Magnet Cove, Arkansas, in the US. The Ice River complex, near Golden, 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 and Greenland
.

Euhedral, transparent crystals are found in northern

Vesuvius
, Italy.

Sodalitite is a type of

extrusive igneous rock rich in sodalite.[16] Its intrusive equivalent is sodalitolite.[16]

History

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

Synthesis

The

mesoporous cage 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 include nitrate,[18] iodide,[19] iodate,[20] permanganate,[21] perchlorate,[22] and perrhenate
.

See also

References

  1. S2CID 235729616
    .
  2. ^ a b Mindat with locations
  3. ^ Webmineral data
  4. ^ a b Handbook of Mineralogy
  5. ISBN 0-471-80580-7
  6. ISBN 978-92-3-100020-1
    .
  7. ^
    S2CID 102105382
    .
  8. ^
    S2CID 93970848
    .
  9. doi:10.1107/S0021889879013492
    .
  10. S2CID 96089478
    .
  11. ^
    doi:10.1107/S0108768184001683
    .
  12. doi:10.3390/min10111042
    .
  13. ISBN 978-1-257-03762-9.[self-published source?
    ]
  14. doi:10.5741/GEMS.45.1.38
    .
  15. ^ Ice River deposit on Mindat
  16. ^
    ISBN 0-521-66215-X
    .
  17. ISBN 978-92-3-100020-1
    .
  18. doi:10.1016/0925-8388(95)02148-5
    .
  19. doi:10.1557/PROC-663-51
    .
  20. doi:10.1016/0040-6031(96)02971-1
    .
  21. doi:10.1016/0144-2449(94)90125-2
    .
  22. doi:10.1016/0920-5861(91)87019-J
    .

External links

Media related to Sodalite at Wikimedia Commons

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