Publication Type:

Journal Article

Authors:

McDonald, Andrew M.; Back, Malcolm E.; Gault, Robert A.; Horváth, László

Source:

The Canadian MineralogistThe Canadian Mineralogist, Mineralogical Association of Canada, Ottawa, ON, Canada, Volume 51, Number 4, p.569-596 (2013)

ISBN:

0008-4476

Keywords:

Albite, alkali metals, alkalic composition, birefringence, Canada, Carbonates, chabazite, coexisting minerals, crystal structure, crystal systems, cubic system, eastern canada, feldspar group, feldspathoid rocks, fluorides, formula, framework silicates, halides, igneous rocks, infrared spectra, iron, lattice parameters, lithium, metals, mineral assemblages, Mont-Saint-Hilaire Quebec, new minerals, optical properties, oxides, paragenesis, Pegmatite, peralkalic composition, perovskite, phosphates, plagioclase, plutonic rocks, polyhedra, quebec, Raman spectra, rare earths, rhodochrosite, Rouville County Quebec, siderite, silicates, space groups, spectra, synchysite, unit cell, x-ray diffraction data, yttrium, zeolite group, zirconium

Abstract:

Peatite-(Y), Li (sub 4) Na1 (sub 2) (Y,Na,Ca,HREE) (sub 12) (PO (sub 4) ) (sub 12) (CO (sub 3) ) (sub 4) (F,OH) (sub 8) , and ramikite-(Y), Li (sub 4) Na (sub 12) (Y,Ca,HREE) (sub 6) Zr (sub 6) (PO (sub 4) ) (sub 12) (CO (sub 3) ) (sub 4) O (sub 4) (OH,F) (sub 4) , are two new minerals discovered in the core of the Poudrette pegmatite at Mont Saint-Hilaire, Quebec. Epitactic-like, euhedral crystals (pseudocubes) of both minerals range from 0.1 to 1 mm in size (average: 0.2 mm), with ramikite-(Y) forming yellowish-white cores (dominant) and peatite-(Y) occurring as thin (< 50 um) pale pink rims. Crystals of peatite-(Y) exhibit the dominant forms pinacoid {100}, {010}, and {001} and the minor forms rhombic prism {110}, {101}, and {011}, with crystals of ramikite-(Y) showing the possible forms pedion {100},{001}, {010}, {010}, {001}, and {001}. The most common associated minerals include albite, rhodochrosite, siderite, chabazite-Na, synchysite-(Ce), and sabinaite. Peatite-(Y) displays a brittle fracture with very good {100}, {010}, and {001} cleavages; ramikite-(Y) has a splintery fracture with possible weak to poor {100}, {010}, and {001} cleavages. Peatite-(Y) has a vitreous luster and ramikite-(Y) has a vitreous to dull luster. Both minerals have a white streak and neither shows any discernible fluorescence under long-, medium-, or short-wave ultraviolet radiation. Both minerals have an approximate Mohs hardness of 3. Peatite-(Y) has a calculated density of 3.62(1) g/cm (super 3) and ramikite-(Y) of 3.60(1) g/cm (super 3) . Both minerals have a very low birefringence (approximately 100), exhibit parallel extinction, and give poor interference figures; the optic sign and measured 2V of both are unknown. Only one refractive index for each could be measured: peatite-(Y), beta = 1.601(1) and for ramikite-(Y), beta = 1.636 (1). Four analyses of peatite-(Y) gave an average (range) of (wt. %): Li (sub 2) O 1.96 (calc.), Na (sub 2) O 12.95 (12.50-13.30), CaO 1.15 (0.98-1.51), Y (sub 2) O (sub 3) 37.32 (37.01-37.52), Gd (sub 2) O (sub 3) 0.61 (0.54-0.74), Dy (sub 2) O (sub 3) 3.08 (2.91-3.44), Ho (sub 2) O (sub 3) 0.67 (b.d.-1.02), Er (sub 2) O (sub 3) 2.88 (2.59-3.15), Tm (sub 2) O (sub 3) 0.28 (b.d.-0.40), Yb (sub 2) O (sub 3) 1.78 (1.67-1.92), ZrO (sub 2) 0.67 (0.63-0.70), ThO (sub 2) 0.37 (b.d.-0.56), P (sub 2) O (sub 5) 27.29 (27.09-27.64), F 4.35 (4.03-4.62), CO (sub 2) 5.79 (calc.), H (sub 2) O 0.31 (calc.), O = F -1.83, total 99.75, corresponding to Li (sub 4) Na (sub 12) (Y (sub 10.06) Na (sub 0.72) Ca (sub 0.62) Dy (sub 0.50) Er (sub 0.46) Yb (sub 0.28) Zr (sub 0 .17) Ho (sub 0.11) Gd (sub 0.10) Tm (sub 0.04) Th (sub 0.04) Tb (sub 0.02) ) (sub Sigma 13.12) (PO (sub 4) ) (sub 11.70) (CO (sub 3) ) (sub 4) [F (sub 6.97) (OH) (sub 1.03) ] (sub Sigma 8) and the simplified formula, Li (sub 4) Na (sub 12) (Y,Na,Ca,HREE) (sub 12) (PO (sub 4) ) (sub 12) (CO (sub 3) ) (sub 4) (F,OH) (sub 8) . For ramikite-(Y), 22 analyses gave an average (range) of (wt. %): Li (sub 2) O 2.01 (calc.), Na (sub 2) O 11.25 (10.32-13.34), CaO 4.15 (4.01-4.27), Y (sub 2) O (sub 3) 16.48 (14.88-18.25), La (sub 2) O (sub 3) 0.11 (b.d.-0.48), Ce (sub 2) O (sub 3) 0.10 (b.d.-0.40), Nd (sub 2) O (sub 3) 0.08 (b.d.-031), Dy (sub 2) O (sub 3) 1.11 (0.96-1.23), Er (sub 2) O (sub 3) 1.18 (1.01-1.36), Yb (sub 2) O (sub 3) 0.57 (0.46-0.68), ZrO (sub 2) 23.40 (22.66-24.70), ThO (sub 2) 0.49 (b.d.-0.70), HfO (sub 2) 0.69 (0.48-0.92), Al (sub 2) O (sub 3) 0.14 (0.09-0.22), P (sub 2) O (sub 5) 28.10 (27.47-28.58), F 0.62 (0.24-0.90), CO (sub 2) 5.92 (calc.), H (sub 2) O 0.92 (calc.), O = F -0.26, total 97.06, corresponding to Li (sub 4) (Na (sub 10.79) Ca (sub 1.21) ) (sub Sigma 12) (Y (sub 4.34) Ca (sub 0.99) Dy (sub 0.18) Er (sub 0.18 ) Yb (sub 0.09) La (sub 0.02) Ce (sub 0.02) Nd (sub 0.01) ) (sub Sigma 5.83) (Zr (sub 5.65) Hf (sub 0.10) Th (sub 0.06) ) (sub Sigma 5.81) [(P (sub 0.98) Al (sub 0.01) ) (sub Sigma 0.99) O (sub 4) ] (sub 12) (CO (sub 3) ) (sub 4) O (sub 4) [(OH) (sub 3.03) F (sub 0.97) ] (sub Sigma 4.00) and the simplified formula, Li (sub 4) ( a,Ca) (sub 12) (Y,Ca,HREE) (sub 6) Zr (sub 6) (PO (sub 4) ) (sub 12) (CO (sub 3) ) (sub 4) O (sub 4) (OH,F) (sub 4) . In both peatite-(Y) and ramikite-(Y), the presence of Li (sub 2) O was confirmed via crystal-structure and LAM-ICP-MS analyses and both H (sub 2) O and CO (sub 2) via results of crystal-structure, infrared, and Raman analyses. Peatite-(Y) crystallizes in space group P222 with a 11.167(2), b 11.164(2), c 11.162(2) Aa, V 1391.7(1) Aa (super 3) , and Z = 1, and ramikite-(Y) in space group P1 with a 10.9977(6), b 10.9985(6), c 10.9966(6) Aa, alpha 90.075(4), beta 89.984(4), gamma 89.969(4) degrees , V 1330.1(1) Aa (super 3) , and Z = 1. The strongest six lines on the X-ray powder-diffraction pattern [d in Aa (I) (hkl)] for peatite-(Y) are: 4.56(57)(211,121,112), 3.95(57)(220,202,022), 3.54(46) (310,301,130), 2.99(83)(321,312,231), 2.63(100)(330,303,033), 2.149(42)(333) and for ramikite-(Y): 11.04(76)( 010, 100, 001), 7.80(79)( 011, 110,101), 6.36(75) (111, 111, 111, 111), 3.89(100)( 022, 220,202), 2.94(98) (132, 123, 231), 2.59(98)( 033,330,303). The crystal structure of peatite-(Y) was refined to R = 3.37% and wR (sub 2) = 9.36% for 3816 reflections and that of ramikite-(Y) to R = 5.13% and wR (sub 2) = 13.06% for 8272 reflections. While not strictly isostructural, both minerals have similar crystal structures dominated by M (sub phi 8) polyhedra (M = Y,Zr; phi = unspecified ligand). These are linked into six-membered, edge- or corner-sharing clusters, which in turn are joined together by PO (sub 4) tetrahedra. Both LiO (sub 6) octahedra and CO (sub 3) groups are positioned within the corner-sharing clusters. Linkages among all these polyhedra produce an open, equidimensional framework structure, with Na occupying the resulting cavities. Although possessing complex crystal structures, both minerals may be considered more simply as homeotypes of body-centered cubic Fe (or CsCl) or, alternatively, as complex derivatives of cation-deficient perovskite-related structures. Both minerals are late-stage products, possibly related to the in situ alteration of the pre-existing mineral assemblage (dawsonite, burbankite-group minerals, sabinaite, muscovite-polylithionite, etc.) present in the core of the Poudrette pegmatite.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2014-004230<br/>peatite<br/>Poudrette Pegmatite<br/>ramikite<br/>sabinaite