Sodalite - Na8Al6Si6O24Cl2

Named from its chemical composition, sodalite was discovered in 1811 in the Ilimaussaq intrusive complex in Greenland. The soldalite group feldspathoids are based on the cubic structure, which is a tektosilicate framework. One half the Si4+ are replaced by Al3+ requiring additional cations for charge balance. The open structure affords an equivalent of two very large cavities per unit cell, which accommodate large cations (Cl-, S2 o SO42-) surrounded by Na+ or Ca2+ in tetrahedral coordination. The large anions and cations distinguish minerals of the sodalite group:

Sodalite: Na8Al6Si6O24Cl2
Hackmanite: Na8Al6Si6O24 (Cl,S)2
Noselite: Na8Al6Si6O24Cl2(SO4)
Hauyne: (Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2
Lazurite (Lapis lazuli): (Na,Ca)8Al6Si6O24(So4,S,Cl)2

The composition of sadalite closely approaches the ideal formula, with minor substitution of Ca+ or K+ for Na+; Fe3+ for Al3+ and S2- or I- for Cl-

The sodalite minerals are characteristic of alkaline, undersaturated igneous rocks. Sadalite is most common in Nepheline Syenite and related rock type in association with Nepheline, cancrinite and alkali feldspar.

Optical properties:
Form: Commonly form euhedral crystals of dodecahedron habit yielding hexagonal sextion
Color: Colorless to pale gray-blue
Relief: Moderate negative relief
Birefringence: Isotropic

sodalite.jpg

Blue soldalite in a syenite.





Bibliography



• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Optical Mineralogy : The Nonopaque Minerals by Phillips / Griffen
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc


Photo
naujaite(19).jpg

Eudialite (high relief and with white-pale pink color) with sodalite (colorless) inclusion in a Naujaite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
naujaite(21).jpg

Eudialite (gray) with sodalite (isotropic) inclusion in a Naujaite. Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(22).jpg

Eudialite (high relief and with white-pale pink color) and aegirine crystals surrounded by sodalite (colorless) in a Naujaite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
naujaite(23).jpg

Eudialite (gray) surrounded by sodalite (isotropic) inclusion in a Naujaite. Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(24).jpg

K-feldspar with sodalite (isotropic) inclusion. Sodalite is surrounded by cancrinite (high interference colors). Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(25).jpg

K-feldspar with sodalite (isotropic) inclusion. Sodalite is surrounded by cancrinite (high interference colors). Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(26).jpg

K-feldspar with sodalite (isotropic) inclusion. Sodalite is surrounded by cancrinite (high interference colors). Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(45).jpg

K-feldspar with sodalite (isotropic) inclusion. Sodalite is surrounded by cancrinite (high interference colors). Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(56).jpg

K-feldspar with sodalite (isotropic) inclusion. Sodalite is surrounded by cancrinite (high interference colors). Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(57).jpg

K-feldspar with sodalite (isotropic) inclusion. Sodalite is surrounded by cancrinite (high interference colors). Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
naujaite(28).jpg

Eudialite (high relief and with white-pale pink color) with sodalite (colorless) inclusion in a Naujaite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
naujaite(29).jpg

Eudialite (gray) with sodalite (colorless) inclusion in a Naujaite. Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
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Sodalite (marked as Sdl), biotite (green) and colorless alkali feldspar. PPL image , 2x (Field of view = 7mm)
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Sodalite (isotropic), biotite and alkali feldspar. XPL image , 2x (Field of view = 7mm)
sienitesodalite777(5).jpg

Sodalite (marked as Sdl), biotite (green) and colorless alkali feldspar. PPL image , 2x (Field of view = 7mm)
sienitesodalite777(6).jpg

Sodalite (isotropic), biotite and alkali feldspar. XPL image , 2x (Field of view = 7mm)
sienitesodalite777(7).jpg

Sodalite (isotropic), titanite and alkali feldspar. XPL image , 2x (Field of view = 7mm)
sienitesodalite777(8).jpg

Sodalite (marked as Sdl), biotite (green) and colorless alkali feldspar. PPL image , 2x (Field of view = 7mm)
sienitesodalite777(9).jpg

Sodalite (isotropic) and alkali feldspar. XPL image , 2x (Field of view = 7mm)
sienitesodalite777(10).jpg

Sodalite (isotropic) and alkali feldspar. XPL image , 2x (Field of view = 7mm)
sienitesodalite777(11).jpg

Sodalite (isotropic), biotite and alkali feldspar. XPL image , 2x (Field of view = 7mm)
sienitesodalite777(12).jpg

Sodalite (marked as Sdl) and colorless alkali feldspar. PPL image , 10x (Field of view = 2mm)
sienitesodalite777(13).jpg

Sodalite (marked as Sdl) and colorless alkali feldspar. PPL image , 10x (Field of view = 2mm)
sienitesodalite777(2).jpg

Sodalite (marked as Sdl) and colorless alkali feldspar. PPL image , 10x (Field of view = 2mm)