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Sodalite
""Sodalith - Rohstein.jpg
General
Category Tectosilicates without zeolitic H2O
"Formula
(repeating unit)
Na
8
(Al
6
Si
6
O
24
)Cl
2
"Strunz classification 9.FB.10
"Crystal system "Cubic
"Crystal class Hextetrahedral (43m)
"H-M symbol: (4 3m)
"Space group P43n
"Unit cell a = 8.876(6) Å; Z = 1
Identification
Color Rich royal blue, green, yellow, violet, white veining common
"Crystal habit Massive; rarely as dodecahedra
"Twinning Common on {111} forming pseudohexagonal prisms
"Cleavage Poor on {110}
"Fracture Conchoidal to uneven
"Tenacity Brittle
"Mohs scale hardness 5.5-6
"Luster Dull vitreous to greasy
"Streak White
"Diaphaneity Transparent to translucent
"Specific gravity 2.27-2.33
Optical properties Isotropic
"Refractive index n = 1.483 - 1.487
"Ultraviolet "fluorescence Bright red-orange "cathodoluminescence and fluorescence under LW and SW UV, with yellowish "phosphorescence; may be "photochromic in magentas
"Fusibility Easily to a colourless glass; sodium yellow flame
"Solubility Soluble in "hydrochloric acid and "nitric acid
Other characteristics Emits "hydrogen sulfide upon fracture
References [1][2][3][4]
Major varieties
Hackmanite "Tenebrescent; violet-red or green fading to white

Sodalite is a rich royal blue tectosilicate "mineral 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.

Discovered in 1811 in the "Ilimaussaq intrusive complex in "Greenland, sodalite did not become important as an ornamental stone until 1891 when vast deposits of fine material were discovered in "Ontario, "Canada.

Contents

Properties[edit]

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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.

It is sometimes referred to as "poor man's lapis" due to its similar color and the fact that is much less expensive. Its name comes from its high sodium content. Most sodalite will "fluoresce orange under "ultraviolet light, and hackmanite exhibits "tenebrescence.[5]

Hackmanite[edit]

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Hackmanite dodecahedron from the Koksha Valley, Afghanistan

Hackmanite is an important variety of sodalite exhibiting "tenebrescence. 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. Much sodalite will also "fluoresce a patchy orange under UV light.

Occurrence[edit]

Sodalite was first described in 1811 for the occurrence in its "type locality in the "Ilimaussaq complex, Narsaq, "West Greenland.[1]

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 undersaturated environments, namely "leucite, "cancrinite and "natrolite. Other associated minerals include "nepheline, titanian "andradite, "aegirine, "microcline, "sanidine, "albite, "calcite, "fluorite, "ankerite and "baryte.[3]

Significant deposits of fine material are restricted to but a few locales: "Bancroft, Ontario, and "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.[6] 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 "Namibia and in the "lavas of "Vesuvius, "Italy.

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This "hippopotamus ornament carved from sodalite demonstrates the mineral's poor "cleavage - cracks can be seen throughout the stone.

History[edit]

The people of the "Caral culture traded for sodalite from the Collao altiplano.[7] Sodalite was also traded for at "Lukurmata. [8]

References[edit]

  1. ^ a b Mindat with locations
  2. ^ Webmineral data
  3. ^ a b Handbook of Mineralogy
  4. ^ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., "ISBN "0-471-80580-7
  5. ^ Rock Roles: Facts, Properties, and Lore of Gemstones By Suzanne Bettonville. p.98
  6. ^ Ice River deposit on Mindat
  7. ^ The Chinchorro culture: a comparative perspective. The archaeology of the earliest human mummification. By Sanz, Nuria, Arriaza, Bernardo T., Standen, Vivien G., editors. p.92
  8. ^ Ancient Titicaca: The Evolution of Complex Society in Southern Peru and North Bolivia, by Charles Stanish, p.162
Stereo image
Right frame 
""Sodalitest.jpg
Small specimen of Sodalite from Brazil.
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