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ADAMSITE-(Y), A NEW SODIUM–YTTRIUM CARBONATE MINERAL SPECIES FROM MONT SAINT-HILAIRE, QUEBEC

Joel D. Grice^1,, Robert A. Gault¹, Andrew C. Roberts² and Mark A. Cooper³

¹ Research Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada
² Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada
³ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

E-mail address: jgrice{at}mus-nature.ca

Adamsite-(Y), ideally NaY(CO₃)₂·6H₂O, is a newly identified mineral from the Poudrette quarry, Mont Saint-Hilaire, Quebec. It occurs as groups of colorless to white and pale pink, rarely pale purple, flat, acicular to fibrous crystals. These crystals are up to 2.5 cm in length and form spherical radiating aggregates. Associated minerals include aegirine, albite, analcime, ancylite-(Ce), calcite, catapleiite, dawsonite, donnayite-(Y), elpidite, epididymite, eudialyte, eudidymite, fluorite, franconite, gaidonnayite, galena, genthelvite, gmelinite, gonnardite, horváthite-(Y), kupletskite, leifite, microcline, molybdenite, narsarsukite, natrolite, nenadkevichite, petersenite-(Ce), polylithionite, pyrochlore, quartz, rhodochrosite, rutile, sabinaite, sérandite, siderite, sphalerite, thomasclarkite-(Y), zircon and an unidentified Na–REE carbonate (UK 91). The transparent to translucent mineral has a vitreous to pearly luster and a white streak. It is soft (Mohs hardness 3) and brittle with perfect {001} and good {100} and {010} cleavages. Adamsite-(Y) is biaxial positive, = 1.480(4), ß = 1.498(2), = 1.571(4), 2V_meas. = 53(3)°, 2V_calc. = 55° and is nonpleochroic. Optical orientation: X = [001], Y = b, Z a = 14° (in ß obtuse). It is triclinic, space group P, with unit-cell parameters refined from powder data: a 6.262(2), b 13.047(6), c 13.220(5) Å, 91.17(4), ß 103.70(4), 89.99(4)°, V 1049.1(5) ų and Z = 4. The strongest six X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 12.81(100)(001), 6.45(70)(002), 4.456(60)(1, 20), 4.291(60)(003), 2.571(60)(005, 043) and 2.050(50)(125,). Electron-microprobe and thermogravimetric analyses, supported by crystal-structure analysis and infrared-absorption spectroscopy, yield Na₂O 8.64, CaO 0.05, Y₂O₃ 22.88, Ce₂O₃ 0.37, Nd₂O₃ 1.41, Sm₂O₃ 1.02, Gd₂O₃ 1.92, Tb₂O₃ 0.56, Dy₂O₃ 3.28, Ho₂O₃ 0.90, Er₂O₃ 2.83, Tm₂O₃ 0.27, Yb₂O₃ 1.04, CO₂ 25.10, H₂O 29.90, total 100.17 wt.%. The empirical formula, based on 12 oxygen atoms, is Na_1.00 (Y_0.72Dy_0.06Er_0.05Gd_0.04Nd_0.03Yb_0.02Sm_0.02Ho_0.02Ce_0.01Tb_0.01Tm_0.01)_0.99 C_2.04H_11.87O₁₂. The calculated density (from the empirical formula) is 2.27 g/cm3, and the measured density is 2.27(2) g/cm³. The structure has been refined to R = 0.046. The structure is layered, with two different carbonate groups, one parallel and one perpendicular to the layering. Slabs of [NaY(CO₃)] are separated by [H₂O] layers. Adjacent [H₂O] layers are only H-bonded together, which gives rise to the perfect {001} cleavage. The mineral is named after Frank Dawson Adams (1859–1942), geologist and professor at McGill University, Montreal.

Keywords: adamsite-(Y), new mineral species, sodium yttrium dicarbonate hexahydrate, crystal structure, Mont Saint-Hilaire, Quebec.

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