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) | |
|---|---|
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| 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 | |
| References | [2][3][4] | 
References
    
- 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.
 - http://rruff.geo.arizona.edu/doclib/hom/thomasclarkitey.pdf Handbook of Mineralogy
 - http://webmineral.com/data/Thomasclarkite-(Y).shtml Webmineral data
 - http://www.mindat.org/min-7336.html Mindat
 
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