| Thomasclarkite-(Y) | |
| Category: | Carbonate mineral |
| Formula: | (Na, Ce)(Y, REE)(HCO3)(OH)3·4(H2O) |
| Imasymbol: | Tcl-Y[1] |
| Molweight: | 375.77 g/mol |
| System: | Monoclinic |
| Class: | Sphenoidal (2) (same H-M symbol) |
| Symmetry: | P2 |
| Color: | White, yellow |
| Habit: | Blocky crystals, pseudo-tetragonal |
| Twinning: | Common on (101) |
| Cleavage: | [010] Perfect, [101] parting |
| Fracture: | Uneven |
| Tenacity: | Very brittle |
| Mohs: | 2–3 |
| Luster: | Vitreous (glassy) |
| Refractive: | nα = 1.40, nβ = 1.540, nγ = 1.540 |
| Opticalprop: | Pseudouniaxial negative 2V (meas.) ≤ 5° |
| Birefringence: | δ = 0.140 |
| Streak: | White |
| Gravity: | 2.30 |
| Diaphaneity: | Translucent to transparent |
| Other: | Radioactive 770 Bq/g |
| References: | [2] [3] [4] |
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.