General Information:
Chemical Formula:
(Na,Ce)(Y,REE)(HCO3)(OH)3·4H2O
Composition:
(Molecular Weight = 375.77 gm)
La,Ce,Pr,Nd,Sm,26.83 % RE
Sodium 4.89 % Na
Cerium 7.46 % Ce
Yttrium 11.83 % Y
Hydrogen 3.22 % H
Carbon 3.20 % C
Oxygen 42.58 % O
Empirical Formula:
Na0.8Ce0.2Y0.5REE0.7(HCO3)(OH)3·4(H2O)
Environment:
Occurs as a late hydrothermal phase in alkaline pegmatite dikes in nepheline syenite.
IMA Status:
Approved IMA 1998 (Dana # Added)
Locality:
Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada.
Name Origin:
Named after Thomas Henry Clark (1893-1996), McGill University, Montreal, Quebec, Canada, noted for his studies of the geology of the St. Lawrence Lowlands.
Physical Properties:
Cleavage:
[010] Perfect, [101] Parting
Color:
white or yellow.
Density:
2.3
Diaphaniety:
Translucent to transparent
Habits:
Pseudo Tetragonal - Crystals show a tetragonal shape., ,
Hardness:
2-3 - Gypsum-Calcite
Luminescence:
Non-fluorescent.
Luster:
Vitreous (Glassy)
Streak:
white
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