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16.34: Ekanite

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    Ekanite
    Chemical composition ThCa2Si8O20
    Crystal system Tetragonal
    Habit Elongated, pebbles.
    Cleavage None
    Hardness 6 - 6.5
    Optic nature Uniaxial -
    Refractive index 1.560 - 1.596
    Birefringence 0.001-0.008
    Dispersion Low
    Specific gravity 3.28
    Lustre Vitreous

    File:Ekaniteed8.jpg

    Figure \(\PageIndex{1}\): A green radioactive ekanite.
    By Chaman Golecha, Gem Testing Laboratory, Jaipur.

    Crystallography

    Tetragonal system.
    Habit: crystals are elongated parallel to the optic axes. Massive as pebles. A rare crystalline non-metamict state of ekanite has also been found.

    Chemical composition

    ThCa2Si8O20: Calcium Thorium Silicate with radioactive elements present. Commonly Uranium, Iron, Lead also present. Metamict and rarer non-metamict ekanite has been found.

    Diagnostics

    Color

    Green, dark brown, light brown, emerald green, also chatoyant, 4-ray, 6-ray varieties also. Straw yellow when pure; dark red (due to inclusions).

    Diaphaneity

    Transparent to translucent.

    Specific gravity

    S.G. 3.08 (impure) and 3.28 - 3.36 (pure) generally 3.28

    Refractometer

    Optic Character: DR, Uniaxial negative.
    Refractive index: 1.560 - 1.568 (may also be 1.590-1.596 or 1.573-1.572) Most commonly 1.596
    Maximum birefringence: 0.001 - 0.008

    Ekanite may test isotropic due to metamictization.

    Spectrum

    May show lines at 630, 658 nm

    Luminescence

    UV fluorescence: generally inert

    Inclusions

    Crystalline inclusions

    Other properties

    Radioactive; enough to activate a Geiger Muller Counter. Non-radioactive material also found. May test isotropic due to radioactivity.

    Phenomena

    Chatoyancy and asterism (4 or 6-pointed stars).

    Treatments

    Heat treatment to restore crystalline state.

    Simulants

    Brazilianite: lower S.G.; R.I., D.R.

    Occurrence

    Geological occurrence:
    Found as water-worn pebbles; first in the gem-gravels of Sri Lanka. Also in glacial syenitic boulder.

    Geographical locations:
    Ehiliayagoda, near Ratnapura in Sri Lanka; Also chatoyant, 4- or 6-ray also. Also at Mt. Ste Hilare; Quebec, Canada; Central Asia; Tombstone mountains, Canada (non-metamict ekanite).


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