Eudialyte Value, Price, and Jewelry Information

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.

Eudialyte

Although lapidaries can cut cabochons and decorative objects from massive or translucent eudialyte crystals, transparent material suitable for faceting is elusive and always small.

Eudialyte Information

Data Value
Name Eudialyte
Colors Shades of brownish red, yellowish brown, reddish orange, orangey pink, pink, red.
Crystallography Hexagonal (trigonal); tabular crystals, may be hexagonal or trigonal; also prismatic, rhombohedral, massive.
Refractive Index 1.591-1.633
Luster Vitreous; greasy; may be dull.
Hardness 5-5.5
Fracture Uneven
Specific Gravity 2.74-2.98
Birefringence 0.003-0.010
Cleavage Basal, indistinct
Dispersion None
Luminescence Not reported.
Luminescence Present No
Transparency Often translucent, rarely transparent.
Absorption Spectrum Not diagnostic.
Formula

Na4( Ca,Fe,Ce,Mn)2ZrSi6O17(OH,CI)2

Pleochroism

Weak, varies with body color: o = colorless/pink/pale yellow; e = pink to colorless.

Optics

= 1.591-1.623; = 1.594-1.633. Uniaxial (+) but sign variable; eucolite reported to be (-).

Optic Sign Uniaxial +, Uniaxial -
Etymology

From Greek words meaning “easy to dissolve,” because of the mineral’s easy solubility in acids.

Occurrence

Nepheline syenites and associated pegmatites.

eudialyte sphere - Russia

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.

Comments

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. 

eudialyte box - Russia

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.

square step-cut eudialyte - Canada

Square step-cut eudialyte, 0.40 cts, 4 mm, Quebec, Canada. © The Gem Trader. Used with permission.

Identifying Characteristics

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.

eudialyte crystals - Russia

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.

Synthetics

Scientists have synthesized eudialytes for geological and petrological research. However, there is no known jewelry use for this lab-created material.

Enhancements

No known gemstone treatments or enhancements.

eudialyte cabochon

Eudialyte cabochon, 42.65 cts, 30.3 x 34 mm. © The Gem Trader. Used with permission.

Sources

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.

eudialyte crystals - Greenland

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:

  • Magnet Cove, Arkansas, United States: rich red color, in feldspar.
  • Sweden: (o = 1.598; e = 1.604; birefringence = 0.004; SG = 2.88)
  • Brazil; Ampasibitika, Madagascar; Pilansberg, South Africa.
eudialyte - Brazil

Eudialyte with alkali feldspar (white), aegirine (black), and biotite (brown), Brazil. Photo by Kevin Walsh. Licensed under CC By 2.0.

Stone Sizes

Lapidaries have faceted eudialytes well under 1 ct from Quebec material. These deep red gems are extremely rare.

  • National Museums of Canada (Ottawa, Ontario): 0.30, 0.40 (intense red, Sheffield Lake, Quebec, Canada).

Care

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.

eudialyte sphere - Canada

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.