Ekanite

Ekanite is an uncommon silicate mineral with chemical formula Ca
2
ThSi
8
O
20
or (Ca,Fe,Pb)
2
(Th,U)Si
8
O
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.

Ekanite
A Cut crystal of Ekanite
General
CategorySilicate mineral
Formula
(repeating unit)
Ca
2
ThSi
8
O
20
or (Ca,Fe,Pb)
2
(Th,U)Si
8
O
20
IMA symbolEk[1]
Strunz classification9.EA.10
Crystal systemTetragonal
Crystal classTrapezohedral (422)
H-M symbol: (4 2 2)
Space groupI422
Identification
ColorGreen, yellow, dark red
Crystal habitPyramidal crystals, granular to massive
CleavageDistinct on {101}
FractureBrittle, uneven
Mohs scale hardness4.5
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.95 - 3.28
Optical propertiesUniaxial (-)
Refractive indexnω = 1.580 nε = 1.568
Birefringenceδ = 0.012
2V angle10 - 15°
Other characteristics Radioactive, metamict
References[2][3][4]

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]

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. Mindat
  3. Handbook of Mineralogy
  4. Ekanite Mineral Data at Webmineral
  5. 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.


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