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Cryolite
Current inventory: 0 gems
 

Chemistry:  Na₃AlF₆  [Sodium Aluminum Fluoride]

Discovered in 1799;   IMA status: Valid (pre-IMA; Grandfathered).
Cryollite is named from the Greek words, kryos meaning frost and lithos meaning stone, hence ice-stone, in allusion to its appearance.

Classification

Mineral Classification:

Halides

Strunz 8th Ed. ID:

3/B.03-30

Nickel-Strunz 10th Ed. ID:

3.CB.15

3 : HALIDES
C : Complex halides
B : Neso-aluminofluorides

Related to:

Kryolithionite-Calcjarlite Series

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals are pseudocubic or short prismatic, striated, to 3 cm; also typically massive or coarsely granular.

Twinning:

Common, according to one or more of 13 distinct twin laws, producing penetration, repeated, or polysynthetic twins.

Physical Properties

Cleavage:

None; Parting on [001] and [110]

Fracture:

Irregular, Uneven

Tenacity:

Brittle

Moh's Hardness:

2.5 - 3.0

Density:

2.95 - 3.00 (g/cm³)

Luminescence:

Weakly thermoluminescent; may fluoresce intense yellow under SW UV, with yellow phosphorescence, pale yellow fluorescence under LW UV.

Radioactivity:

Not Radioactive

Other:

Slightly soluble in water

Optical Properties

Color:

Colorless, Gray, White, Reddish brown, Brownish black

Transparency:

Transparent to Translucent

Luster:

Vitreous, Greasy, Pearly

Refractive Index:

1.3385 - 1.340  Biaxial ( + )

Birefringence:

0.0010 - 0.0011

Dispersion:

None; r < v

Pleochroism:

X = colorless; Y = colorless; Z = colorless

Occurances

Geological Setting:

A late-stage mineral in some granite pegmatites; in tin-bearing alkalic granites; a vapor-phase mineral along fractures and in the groundmass of some fluorine-rich, topaz-bearing rhyolites; in pods in a carbonatite vein cutting fenitized biotite gneiss. Also as a rare authigenic component of the marlstones and shales of the Green River Formation.

Common Associations:

Chiolite, Feldspar Group, Fluorite, Pachnolite, Quartz, Topaz

Type Locality:

Cryolite deposit, Ivittuut (Ivigtut), Arsuk Firth, Arsuk, Kitaa Province (West Greenland), Greenland

Year Discovered:

1799

View mineral photos:

Cryolite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Cryolite is a very rare gem since gem quality crystals are very rare and only available from one source. It is typically colorless and usually has a slightly sleepy look. The index of refraction of Cryolite is 1.3385, which is very close to the index of refraction of water (1.3328). The result is that if you put a clean, colorless gem or crystal of Cryolite in water, it will essentially disappear.

Sources of Cryolite include the Ivigtut area of Greenland and also at the foot of Pikes Peak at Creede, Colorado, USA, Mont Saint-Hilaire and Francon Quarry, Montreal, Quebec, Canada and at Miask, Russia. Gem quality crystals are usually only from Francon Quarry.

  
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