Thomasclarkite-(Y)

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

Thomasclarkite-(Y)
General
Category	Carbonate mineral
Formula	(Na, Ce)(Y, REE)(HCO3)(OH)3·4(H2O)
IMA symbol	Tcl-Y[1]
Crystal system	Monoclinic
Crystal class	Sphenoidal (2) (same H-M symbol)
Space group	P2
Identification
Formula mass	375.77 g/mol
Color	White, yellow
Crystal habit	Blocky crystals, pseudo-tetragonal
Twinning	Common on (101)
Cleavage	[010] Perfect, [101] parting
Fracture	Uneven
Tenacity	Very brittle
Mohs scale hardness	2–3
Luster	Vitreous (glassy)
Streak	White
Diaphaneity	Translucent to transparent
Specific gravity	2.30
Optical properties	Pseudouniaxial negative 2V (meas.) ≤ 5°
Refractive index	nα = 1.40, nβ = 1.540, nγ = 1.540
Birefringence	δ = 0.140
Other characteristics	Radioactive 770 Bq/g
References	[2][3][4]

See also

• List of minerals
• List of minerals named after people