16.34: Ekanite
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|---|---|
| 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 |
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).