Thomasclarkite-(Y) (Type Locality)
Na(Y,REE)(HCO₃)(OH)₃ · 4H₂O

     Formerly UK-93, Thomasclarkite is another member of the long list of REE species from Mont Saint-Hilaire. Originally rare, some more abundant finds were made in '98 and '99.

PHYSICAL CHARACTERISTICS:

Color ranges from white to yellow.
Luster is vitreous.
Diaphaneity is transparent to translucent.
Crystal System is monoclinic;PC2.
Crystal Habits include blocky, well-formed crystals to 2mm.
Cleavage {010} is perfect, and good parting {1010}.
Fracture is uneven.
Hardness is 2 - 3.
Specific Gravity is approximately 2.30 g/cm³.
Streak is white.
Associated Minerals include aegirine, albite, analcime, ancylite-(Ce),
   astrophyllite, calcite, catapleiite, dawsonite, elpidite, epididymite,
   franconite, gaidonnayite, galena, genthelvite, microcline, molybdenite,
   natrolite, petersenite-(Ce), polylithionite, pyrochlore, rhodochrosite,
   rutile, sérandite, siderite, sphalerite, zircon and an unidentified
   NaREE carbonate.
Distinguishing Features: Crystal habit and color.
Origin: Named in 1997 after Thomas Henry Clark (1893-1966),
   McGill University geology professor.

CLASSIFICATION:

REFERENCES:
CanMin 36:1295-1301 (1998)

DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:

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