Thomasclarkite

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Thomasclarkite-(Y)
Category Mineral
Chemical formula (Na,Ce)(Y,REE)(HCO3)(OH)3·4(H2O)
Identification
Molecular Weight 375.77 gm
Color White, Yellow
Crystal habit Blocky crystals pseudo-tetragonal
Crystal system Monoclinic - Sphenoidal
Twinning Common on (101)
Cleavage [010] Perfect, [101] Parting
Fracture Brittle - Uneven - Very brittle fracture producing uneven fragments
Mohs Scale hardness 2-3
Luster Vitreous (Glassy)
Refractive index α= 1.40, β= 1.540, γ= 1.540
Optical Properties pseudouniaxial negative 2V(meas.) = 5°
Birefringence δ = 0.140
Streak white
Specific gravity 2.30
Diaphaneity Translucent to transparent
Other Characteristics Radioactivity 770 Bq/g

Thomasclarkite-(Y) is a very rare mineral which was known as UK-93 until 1997, when it was renamed in honour of Dr. Thomas H. Clark (1893-1996), McGill University professor. The mineral is one of many rare earth element minerals from Mont Saint-Hilaire. Rare occurrence in an alkalic pegmatite dike in an intrusive gabbro-nepheline syenite.

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