Rectangular mix-cut ekanite, 9.74 cts, 11.9 x 14.5 mm, Sri Lanka. © The Gem Trader. Used with permission.
Ekanite
A relative newcomer to the world of gemstones, ekanite is rare and usually quite radioactive.
Ekanite Information
| Data | Value |
|---|---|
| Name | Ekanite |
| Colors | Green from light to emerald, brown from light to dark, yellowish, dark red, blackish, colorless. |
| Crystallography | Tetragonal. Crystals elongated parallel to long crystal axis; massive pebbles. May become amorphous (metamict) due to radiation. |
| Refractive Index | 1.572-1.596 |
| Luster | Vitreous |
| Hardness | 4.5-6.5 |
| Fracture | Uneven to irregular |
| Specific Gravity | 3.28-3.32 |
| Birefringence | 0.001-0.006 |
| Cleavage | None |
| Luminescence | Not diagnostic |
| Transparency | Transparent to translucent |
| Absorption Spectrum | May show lines at 6300 and 6580. |
| Phenomena | Asterism, chatoyancy, Tyndall scattering. |
| Formula |
(Th,U)(Ca,Fe,Pb)2Si8O20 |
| Optics |
o = 1.573; e = 1.572. Uniaxial (-). Gems usually 1.590-1.596. |
| Optic Sign | Uniaxial - |
| Etymology |
After F. L. D. Ekanayake, the discoverer of this gem. |
| Occurrence |
Gem gravels, volcanic ejecta, placer deposits, and glacial erratic syenitic boulders. |
| Inclusions |
Platelets, rods, two-phase inclusions (sometimes occurring in rows at right angles to create cross-like inclusions), crystals (sometimes with halos), bubbles. |
Ekanite: Sri Lanka (~ 0.5 ct). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Comments
The gemologist F. L. D. Ekanayake discovered ekanite as two cabochon-cut gemstones in a market in Colombo, Sri Lanka in 1953. When he examined these unknown stones, he found they had unusual optical and physical properties. He later discovered the source of these and other similar stones in gravel beds in Eheliyagoda, near Ratnapura, Sri Lanka. In 1961, scientists confirmed the mineral as a new species and named it ekanite after its discoverer.
Other sources of ekanite have emerged, but it remains a rare gemstone. More stones undoubtedly exist, perhaps misidentified and sold as other Sri Lankan gems. However, the total number of gems is still a mere handful.
Although ekanite has a tetragonal crystal system, it’s usually metamict as a result of its uranium (U) and thorium (Th) content. This means it loses its crystalline structure due to radioactivity, becoming amorphous, like glass. Other gemstone properties may also vary depending on the degree of radiation damage.
Identifying Characteristics
The first ekanite gems discovered displayed asterism in the form of a 4-ray star effect. This phenomenal effect is rare, but in addition, 6-ray and 8-ray stars have since been discovered. Ekanites may also display chatoyancy (cat’s eyes) as well as Tyndall scattering.
Small, crystalline (non-metamict) ekanites have been found in Canada.
Sources
Sri Lanka has produced most known ekanites, as translucent green pebbles from gem gravels in Eheliyagoda and in placer deposits from Okkampitiya.
Other notable sources include the following locations:
- Quebec (metamict); Tombstone Mountains, Yukon (crystalline), Canada.
- Monte Somma, Vesuvius, Italy; Kyrgyzstan; Myanmar; Tulare County, California, United States.
Baguette-cut ekanite, 3.22 cts, 12.7 x 6.6 mm, Myanmar. © The Gem Trader. Used with permission.
Stone Sizes
The London Gem Labs tested a 43.8-ct stone in 1975. A 351-ct rough has also been reported.
In 1999, a 161-ct star stone cabochon was examined by the GIA. This may have been the record holder for largest finished ekanite gem until 2016. A new title holder, a 498-ct gem from Welimada, Sri Lanka, has been reported.
Radioactivity
Metamict ekanite may be strongly radioactive, so jewelry use isn’t recommended.
Test any ekanite you’re going to handle or store with a Geiger counter. You can also use the radioactivity chart on this site to estimate how much exposure in mRem per hour ekanites of different sizes may cause if held in hand.
For storage and display, keep any samples enclosed and separated from other gems (radiation may affect their color) and use radon detectors to monitor the buildup of radon gases in the storage container as well as the room.
Estimating Exposure
Please note: the average annual estimated exposure in the U.S. from background radiation, medical sources, and consumer products is 360 mRem. To put this in perspective, at almost 500 cts (about 100 g), a little over 20 hours of holding the world’s largest ekanite would alone match the average annual estimated exposure. A 5-ct ekanite (1 gram) would take a little over 83 days of close contact to match the annual average estimate.
To safely handle, store, and cut ekanite, follow the recommendations for radioactive materials in our safety guide. You can find additional safety information here.
Ekanite mineral specimen, 52.66 cts, 2.5 cm, Eheliyagoda gem pits, Sri Lanka. Photo courtesy of liveauctioneers.com and Nest Egg Auctions.
IGS Newsletter