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Chemical formula(Na,Ce)(Y,REE)(HCO3)(OH)3·4(H2O)
Molecular Weight375.77 gm
ColorWhite, Yellow
Crystal habitBlocky crystals pseudo-tetragonal
Crystal systemMonoclinic - Sphenoidal
TwinningCommon on (101)
Cleavage[010] Perfect, [101] Parting
FractureBrittle - Uneven - Very brittle fracture producing uneven fragments
Mohs Scale hardness2-3
LusterVitreous (Glassy)
Refractive indexα= 1.40, β= 1.540, γ= 1.540
Optical Propertiespseudouniaxial negative 2V(meas.) = 5°
Birefringenceδ = 0.140
Specific gravity2.30
DiaphaneityTranslucent to transparent
Other CharacteristicsRadioactivity 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.

See also


  • Webmineral
  • Mont Saint-Hilaire
  • Mindat with location data
  • Mineral Data Publishing
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Thomasclarkite". A list of authors is available in Wikipedia.
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