Home > Mineral Abstracts > CanMin Vol. 36, pp. 1295-1301 (1998)




Vol. 36, pp. 1295-1301 (1998)



Thomasclarkite-(Y), a new sodium - rare-earth-element bicarbonate mineral species from Mont Saint-Hilaire, Quebec


Joel D. Grice1and Robert A. Gault
Research Division, Canadian Museum of Nature,
P.O. 3443, Station D, Ottawa, Ontario K1P 6P4



1E-mail address: jgrice@mus-nature.ca


ABSTRACT

     Thomasclarkite-(Y), ideally Na(Y,REE)(HCO3)(OH)3 · 4H2O, is a newly identified mineral species from Mont Saint-Hilaire, Quebec. It occurs as individual, well-formed, blocky, white-to-yellow crystals up to 2 mm in length. 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. The transparent to translucent mineral has vitreous luster and a white streak. It is soft (Mohs hardness 2-3) and brittle, with an uneven fracture,
a perfect {010} cleavage and good {1010} parting. Merohedral twinning on {101} is ubiquitous. Thomasclarkite-(Y) is pseudo-uniaxial negative,
w = 1.540(4) and e = 1.40(2). It is monoclinic, space group P2, a 4.566(1), b 13.018(6), c 4.566(2) Å, B 90.15(3)°, V270.2(2) Å3 and Z = 1.

     The strongest X-ray powder-diffraction lines [d in Å (I)(hkl)] are:


12.97(10)(010)
6.52(3)(020)
4.57(3)(100,001)
4.32(5)(110,011)

3.223(3)(-101,101)
3.133(5)(-111,111)
2.593(3)(-131,131)
2.035(3)(201,102)

 
2.016(4)(230,032)
1.844(3)(231,132)


     The infrared spectrum is given. Two electron-microprobe analyses and a thermogravimetric analysis gave:


Na2O - 6.72
(6.20 - 7.24)
CaO - 0.33
(0.35 - 0.32)
Y2O3 - 14.52
(14.97 - 14.07)
La2O3 - 8.63
(8.54 - 8.72)

Ce2O3 - 17.11
(18.44 - 15.79)
Pr2O3 - 1.92
(1.94 - 1.90)
Nd2O3 - 5.63
(5.60 - 5.66)
Sm2O3 - 1.22
(1.27 - 1.17)

Gd2O3 - 1.22
(1.13 - 1.31)
Dy2O3 - 2.04
(2.08 - 2.00)
Er2O3 - 2.20
(2.20 - 2.20)
Yb2O3 - 1.32
(1.45 - 1.19)

ThO2 - 0.54
(0.48 - 0.60)
F - 0.17
(0.35 - 0.00)
CO2 - 12.00
H2O - 26.60


 
O = F - -0.07
for a total of 102.10 wt.%.


     The empirical formula, based on 10 anions and one atom of C, is :


(Na0.80Ce0.18Ca0.02)S1.00(Y0.48La0.20Ce0.21Pr0.04Nd0.12Sm0.03


Gd0.03Dy0.04 Er0.04Yb0.03)S1.22(HCO3)[O6.97F0.03]H9.93.


     Dcalc. = 2.34 g/cm3 and Dmeas. = 2.30(2) g/cm3. The structure has been refined to R = 0.055 using a twinned crystal. The structure is layered on {010}. One layer consists of [HCO3]- groups oriented perpendicular to (010) and H-bonded to a H2O layer. A second layer consists of (Yr8) polyhedra and (Nar6) polyhedra which are H-bonded to the H2O layer. In other bicarbonate minerals, the H-bonding is between the CO3 groups forming chains, whereas thomasclarkite-(Y), the H-bonding is directed toward the H2O groups.


© 1998  The Canadian Mineralogist