Ekanite

Silicate mineral of the steacyite group
(repeating unit)Ca
2ThSi
8O
20 or (Ca,Fe,Pb)
2(Th,U)Si
8O
20IMA symbolEk[1]Strunz classification9.EA.10Crystal systemTetragonalCrystal classTrapezohedral (422)
H-M symbol: (4 2 2)Space groupI422IdentificationColorGreen, yellow, dark redCrystal habitPyramidal crystals, granular to massiveCleavageDistinct on {101}FractureBrittle, unevenMohs scale hardness4.5LusterVitreousStreakWhiteDiaphaneityTransparent to translucentSpecific gravity2.95 – 3.28Optical propertiesUniaxial (−)Refractive indexnω = 1.580 nε = 1.568Birefringenceδ = 0.0122V angle10 – 15°Other characteristics Radioactive, metamictReferences[2][3][4]

Ekanite is an uncommon silicate mineral with chemical formula Ca
2ThSi
8O
20 or (Ca,Fe,Pb)
2(Th,U)Si
8O
20. It is a member of the steacyite group. It is among the few gemstones that are naturally radioactive. Most ekanite is mined in Sri Lanka, although deposits also occur in Russia and North America. Clear and well-colored stones are rare as the radioactivity tends to degrade the crystal matrix over time in a process known as metamictization.

The type locality is Eheliyagoda, Ratnapura District, Sabaragamuwa Province, Sri Lanka,[2] where it was first described in 1955 by F. L. D. Ekanayake, a Sri Lankan scientist,[5][6] and it is named after him.[5]

In Sri Lanka the mineral specimens occur as detrital pebbles. In the Tombstone Mountains of Yukon, Canada, the mineral is found in a syenitic glacial erratic boulder.[3] In the Alban Hills of Italy it is found in volcanic ejecta.[2]

Ekanite can be uranium-lead dated with ekanite from Okkampitiya in the Monaragala District of Sri Lanka being dated to around 560 million years old.[7]


References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Mindat
  3. ^ a b Handbook of Mineralogy
  4. ^ Ekanite Mineral Data at Webmineral
  5. ^ a b New Minerals, American Mineralogist
  6. ^ B. W. Andeson; G. F. Claringbull; R. J. Davis & D. K. Hill (1961). "Ekanite, a new metamict mineral from Ceylon". Nature. 190 (4780): 997. Bibcode:1961Natur.190..997A. doi:10.1038/190997a0. S2CID 4152735.
  7. ^ Wade, Andrew D.; Beckett, Ronald G.; Conlogue, Gerald J.; Gonzalez, Ramon; Wade, Ronn; Brier, Bob (2015). "MUMAB : A Conversation With the Past". The Anatomical Record. 298 (6): 954–973. doi:10.1002/ar.23152. ISSN 1932-8486. PMID 25755117.


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