16.34: Ekanite

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gemology
Gemology Project

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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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