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Category Silicate mineral
(repeating unit)
Ca2ThSi8O20 or (Ca,Fe,Pb)2(Th,U)Si8O20
Strunz classification 9.EA.10
Crystal system Tetragonal
Crystal class Trapezohedral (422)
H-M symbol: (4 2 2)
Space group I422
Color Green, yellow, dark red
Crystal habit Pyramidal crystals, granular to massive
Cleavage Distinct on {101}
Fracture Brittle, uneven
Mohs scale hardness 4.5
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.95 - 3.28
Optical properties Uniaxial (-)
Refractive index nω = 1.580 nε = 1.568
Birefringence δ = 0.012
2V angle 10 - 15°
Other characteristics Radioactive, metamict
References [1][2][3]

Ekanite is an uncommon silicate mineral with chemical formula: Ca2ThSi8O20 or (Ca,Fe,Pb)2(Th,U)Si8O20. 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 Ehiliyagoda, Ratnapura District, Sabaragamuwa Province, Sri Lanka,[1] where it was first described in 1955 by F. L. D. Ekanayake,[4][5] and it is named after him.[4]

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.[2] In the Alban Hills of Italy it is found in volcanic ejecta.[1]


  1. ^ a b c Mindat
  2. ^ a b Handbook of Mineralogy
  3. ^ Ekanite Mineral Data at Webmineral
  4. ^ a b New Minerals, American Mineralogist
  5. ^ 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.