Oval-cut eudialyte, 0.52 cts, 6.4 x 4.7 x 3.0 mm, Mont St. Hilaire, Quebec, Canada. © ARK Rare Gems. Used with permission.
Although lapidaries can cut cabochons and decorative objects from massive or translucent eudialyte crystals, transparent material suitable for faceting is elusive and always small.
| Data | Value |
|---|---|
| Name | Eudialyte |
| Colors | Shades of brownish red, yellowish brown, reddish orange, orangey pink, pink, red. |
| Hardness | 5-5.5 |
| Fracture | Uneven |
| Cleavage | Basal, indistinct |
| Formula | Na4( Ca,Fe,Ce,Mn)2ZrSi6O17(OH,CI)2 |
| Crystallography | Hexagonal (trigonal); tabular crystals, may be hexagonal or trigonal; also prismatic, rhombohedral, massive. |
| Crystallographic Forms | |
| Refractive Index | 1.591-1.633 |
| Birefringence | 0.003-0.010 |
| Dispersion | None |
| Luminescence | Not reported. |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic. |
| Pleochroism | Weak, varies with body color: o = colorless/pink/pale yellow; e = pink to colorless. |
| Optics | o = 1.591-1.623; e = 1.594-1.633. Uniaxial (+) but sign variable; eucolite reported to be (-). |
| Optic Sign | Uniaxial +, Uniaxial - |
| Luster | Vitreous; greasy; may be dull. |
| Specific Gravity | 2.74-2.98 |
| Transparency | Often translucent, rarely transparent. |
| Etymology | From Greek words meaning “easy to dissolve,” because of the mineral’s easy solubility in acids. |
| Occurrence | Nepheline syenites and associated pegmatites. |
This “Dragon’s Blood” eudialyte sphere has an intense carmine red color with green-black aegirine accents. 3” diameter, Khibiny Massif, Kola Peninsula, Murmanskaja Oblast’, Northern Region, Russia. Photo courtesy of liveauctioneers.com and Heritage Auctions.
Eudialyte, also spelled eudialite or eudyalite, belongs to a mineral group of the same name. Although this group of trigonal cyclosilicates contains many members, eudialytes are the only ones likely to be encountered as gemstones. Eudialytes can have deep to bright red colors, and gem cutters commonly fashion them into cabochons and carved objects, especially spheres. These objects are often cut to also feature a combination of black and white minerals, especially black aegirine crystals, which adds a striking contrast to the red stone.
A box made from carved red eudialyte and black and white matrix (even the feet), 4.50 x 2.75 x 1.50 inches, Kola Peninsula, Murmanskaja Oblast’, Northern Region, Russia. Photo courtesy of liveauctioneers.com and Heritage Auctions.
While uncut eudialyte crystals are popular specimens for mineral collections, faceted gemstones would make very rare, very prized additions.
Eudialytes are mildly radioactive, but wearing or handling pieces under 5 cts (1 gram) should pose no health risks. On the other hand, holding a eudialyte sphere of 5,000 cts (1 kg) — a very large piece, indeed — would expose you to 2.40 mREM per hour. To put that in perspective, the average annual estimated radiation exposure in the U.S. from background radiation, medical sources, and consumer products is 360 mRem.
The radioactivity chart on this site can help you estimate exposure for holding different sizes of eudialytes. You can also use a Geiger counter to measure the radioactivity of a specific gem or sample.
Some calcium-rich eudialytes, known as eucolites, have a uniaxial (-) optic character. These may also have higher refractive indices (RI) and specific gravity (SG) values than other eudialytes.
Eudialytes, 4.5 x 3.1 x 2.9 cm, Khibiny Massif, Kola Peninsula, Murmanskaja Oblast’, Northern Region, Russia. © Rob Lavinsky, www.iRocks.com. Used with permission.
Scientists have synthesized eudialytes for geological and petrological research. However, there is no known jewelry use for this lab-created material.
No known gemstone treatments or enhancements.
Eudialyte cabochon, 42.65 cts, 30.3 x 34 mm. © The Gem Trader. Used with permission.
The most notable source of eudialyte gem material, particularly for cabochons and carvings, is the Kola Peninsula in Russia.
Two localities in Quebec, Canada produce red, facetable eudialytes: Mont St. Hilaire (o = 1.596, e = 1.600; birefringence = 0.004); Kipawa Complex, Sheffield Lake, Temiscamingue County.
Greenland has multiple sites, such as Qaqortoq (Julienhaab District), which produces crystals up to 1” in length.
Chocolate (brownish red) eudialytes with aegirine, 6.1 x 5.3 x 4.3 cm, Kangerdluarssuq Firth, Ilimaussaq complex, Narsaq, Kitaa (West Greenland) Province, Greenland. © Rob Lavinsky, www.iRocks.com. Used with permission.
Other notable sources include the following locations:
Eudialyte with alkali feldspar (white), aegirine (black), and biotite (brown), Brazil. Photo by Kevin Walsh. Licensed under CC By 2.0.
Lapidaries have faceted eudialytes well under 1 ct from Quebec material. These deep red gems are extremely rare.
Although eudialytes smaller than 5 cts are safe to wear, you should still take extra precautions when storing radioactive gems of any size. Keep eudialytes enclosed and separated from other gems, since radiation may gradually alter their color. Over time, even mildly radioactive materials release radon gases. Use radon detectors to monitor the buildup of radon gases in the storage container as well as the room.
To safely store and cut eudialyte, follow the recommendations for radioactive materials in our faceting safety guide.
With a hardness of 5 to 5.5, eudialyte jewelry stones should have protective settings to shield them from scratches. Occasional use is also advisable.
Eudialytes are soluble in acids. Clean them only with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more care recommendations.
A maroon red eudialyte sphere with patches of black aegirine and white feldspar, 2” in diameter, Canada. Photo courtesy of liveauctioneers.com and Heritage Auctions.
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