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) |
|---|
| 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 | [1][2][3] |
|---|