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 (repeating unit)	(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

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. http://rruff.geo.arizona.edu/doclib/hom/thomasclarkitey.pdf Handbook of Mineralogy
3. http://webmineral.com/data/Thomasclarkite-(Y).shtml Webmineral data
4. http://www.mindat.org/min-7336.html Mindat

• Mont Saint-Hilaire