Oval-cut cryolite, 0.66 cts, 6.64 mm x 4.48 mm, Ivigtut, Greenland. © Rob Lavinsky, www.iRocks.com. Used with permission.
Typically colorless with a “sleepy” look, cryolite is rarely found in nature. Rough suitable for gem faceting is extremely scarce. However, the synthetic version of this mineral has many industrial uses.
| Data | Value |
|---|---|
| Name | Cryolite |
| Colors | Colorless, white, brownish, reddish; rarely gray to black. |
| Hardness | 2.5 |
| Fracture | Uneven |
| Cleavage | None |
| Formula | Na3AlF6 |
| Crystallography | Monoclinic. Crystals cuboidal and prismatic; usually massive. |
| Crystallographic Forms | |
| Refractive Index | 1.338-1.339 |
| Birefringence | 0.001; almost isotropic. |
| Dispersion | 0.024 (approximately) |
| Luminescence | Weak thermoluminescence. Some specimens may fluoresce intense yellow under shortwave UV, with yellow phosphorescence, and pale yellow fluorescence under longwave UV. Specimens from Mont Saint-Hilaire, Canada may fluoresce pale blueish white under shortwave UV. |
| Luminescence Present | Yes |
| Absorption Spectrum | Not diagnostic |
| Pleochroism | None |
| Optics | a = 1.338; β = 1.338; γ = 1.339. Biaxial (+), 2V = 43°. |
| Optic Sign | Biaxial + |
| Luster | Vitreous to greasy |
| Specific Gravity | 2.97 |
| Transparency | Transparent (rarely) to translucent |
| Luminescence Type | Fluorescent, Phosphorescent, UV-Long, UV-Short |
| Etymology | From the Greek kryos, “frost,” and lithos, “stone,” hence “ice stone,” in allusion to its appearance. |
| Occurrence | Occurs in alkalic rocks, granite pegmatites. |
Cryolite crystals with minor brown siderite patches. Ivigtut Mine, Arsuk Fjord, Sermersooq, Greenland. Photo by Kelly Nash. Licensed under CC By 3.0.
The mineral cryolite has been used in the aluminum industry, first as an ore itself and then as a flux to extract aluminum from other ores more efficiently. Cryolite has proven to have many other industrial uses, from ceramics to pesticides. However, most of the material used today is synthetic.
Glassmakers can add cryolite to glass to create an opaque, white color. So-called “cryolite glass,” invented in Germany in 1835, proved very popular as a material for prosthetic eyes because of the naturalistic results. Cryolite glass eyes in presentation case, made in Lauscha, Thuringia, Germany, ca 1900. Photo courtesy of liveauctioneers.com and Auction Team Breker.
Oval-cut cryolite, 0.66 cts, 6.4 x 5.6 mm, Mont Saint-Hilaire, Quebec, Canada. © The Gem Trader. Used with permission.
With a hardness of just 2.5 on the Mohs scale, cryolites would make a very impractical choice for jewelry wear. A copper coin (hardness of 3) could accidentally scratch it. Household dust, a far more pervasive hazard, has a hardness of 7 and can easily leave scratches on cryolites.
Typically colorless and very rarely transparent, cryolites seldom attract the attention of adventurous faceters or curious gemstone enthusiasts. You’re more likely to find cryolites, faceted or in natural forms, in a mineral or rare gem collection than a jewelry collection.
Cryolite, the “ice stone,” and chiolite, the “snow stone,” can appear very similar. They also occur in the same locations and have many gemological properties that differ only slightly. Both are rarely faceted, but chiolite is a rarer mineral.
Chiolite is a harder material (3.5 to 4), but scratch testing on finished gems isn’t recommended. Conduct this test only as a last resort for identification.
The quickest way to distinguish these gems is to use a polariscope to find their optic character. Cryolites are biaxial +; chiolites are uniaxial -. You can also use a refractometer to identify optic character.
Since abundant sources of natural cryolites are very scarce, scientists have synthesized this mineral for a wide variety of uses. However, there’s no known jewelry use for this lab-created material. Cryolite’s softness and limited visual appeal make a viable jewelry market for synthetics very improbable.
Cryolites usually receive no gemstone enhancements.
Cryolite was found in commercially significant quantities only in Greenland and only in one locality, the Ivigtut mine. This source is now exhausted.
Other notable sources of cryolite include the following:
This crystal specimen features translucent, light gray cryolite and iron oxides. 7.3 x 4.8 x 4.2 cm. St Peters Dome, Cheyenne District, El Paso Co., Colorado, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
Lapidaries could cut large cabochons from abundant material, such as what Greenland produced. However, facetable rough is quite rare and will only yield tiny gems.
Clean cryolites with a soft brush, mild detergent, and warm water. However, please note that cryolites are slightly soluble in water. Don’t submerge these gems in water. After cleaning, carefully pat them dry. (Don’t wipe them dry). For more care recommendations, consult our gemstone jewelry care guide.
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