Adamsite-(Y), a new sodium-yttrium carbonate mineral species from Mont Saint-Hilaire, Quebec

Adamsite-(Y), ideally NaY(CO3)(2 .)6H(2)O, is a newly identified mineral fr om the Poudrette quarry, Mont Saint-Hilaire, Quebec. It occurs as groups of colorless to white and pale pink, rarely pale purple, flat, acicular to fi brous crystals. These crystals are up to 2.5 cm in length and form spherica l radiating aggregates. Associated minerals include aegirine, albite, analc ime, ancylite-(Ce), calcite, catapleiite, dawsonire, donnayite-(Y), elpidit e, epididymite, eudialyte, eudidymite, fluorite, franconite, gaidonnayite, galena, genthelvite, gmelinite, gonnardite, horvathite-(Y), kupletskite, le ifite, microcline, molybdenite, narsarsukite, natrolite, nenadkevichite, pe terseniie-(Ce), polylithionite, pyrochlore, quartz, rhodochrosite, rutile, sabinaite, serandite, siderite, sphalerite, thomasclarkite-(Y), zircon and an unidentified Na-REE carbonate (UK 91). The transparent to translucent mi neral 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} cleavag es. Adamsite-(Y) is biaxial positive, alpha = 1.480(4), beta = 1.498(2), ga mma = 1.571(4), 2V(meas.) = 53(3)degrees, 2V(calc.) = 55 degrees and is non pleochroic. Optical orientation: X = [001], Y = b, Z Lambda a = 14 degrees (in beta obtuse). It is triclinic, space group P (I) over bar, with unit-ce ll parameters refined from powder data: a 6.262(2), b 13.047(6), c 13.220(5 ), Angstrom, alpha 91.17(4), beta 103.70(4), gamma 89.99(4)degrees, V 1049. 1(5) Angstrom (3) and Z = 4. The strongest six X -ray powder-diffraction li nes [d in Angstrom (I)(hkl)] are: 12.81(100)(001), 6.45(70)(002), 4.456(60) ((1) over bar(2) over bar1,(1) over bar 20), 4.291(60)(003), 2.571(60)(005, 043) and 2.050(50)(125,(1) over bar 26). Electron-microprobe and thermogra vimetric analyses, supported by crystal-structure analysis and infrared-abs orption spectroscopy, yield Na2O 8.64 CaO 0.05, Y2O3 22.88, Ce2O3 0.37, Nd2 O3 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 (Y0.72Dy0.06Er0.05G d0.04Nd0.03Yb0.02Sm0.02 Ho0.02Ce0.01Tb0.01Tm0.01)(Sigma0.99) C2.04H11.87O12 . The calculated density (from the empirical formula) is 2.27 g/cm(3), 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 se parated 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 Universit y, Montreal.