Micheelsenite, (Ca,Y)(3)A1(PO3OH,CO3)(CO3)(OH)(6) center dot 12H(2)O, a new mineral from Mont Saint-Hilaire, Quebec, Canada and the Nanna pegmatite, Narsaarsuup Qaava, South Greenland

Micheelsenite, a new member of the ettringite group, is found in pegmatites , so-called silicate cavities, seams in hornfels and marble xenoliths at th e Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada and at the Nanna peg matite, Narsaarsuup Qaava, South Greenland. It occurs as acicular to fibrou s crystals in loosely packed radiating groups and as matted fibres. At Mont Saint-Hilaire, the mineral occurs in association with aegirine, albite, an cylite-(Ce), catapleiite, fluorite, microcline, monteregianite-(Y), natroli te, nenadkevichite, rhodochrosite and serandite (pegmatites) or natrolite, titanite, calcite and pyrite (seams in hornfels). At the Nanna pegmatite th e mineral occurs with aegirine, astrophyllite, analcime, calcio-ancylite-(C e), catapleiite, fluorite, galena, gibbsite, leucophanite, microcline, natr olite, nafertisite, orthoclase, polylithionite, sodalite var. hackmanite an d todorokite. The mineral is colorless to white, transparent to opaque with a vitreous luster. It has a hardness of 3(1)/(2) - 4, is brittle with a sp lintery fracture and has good {10 (1) over bar0} and {0001} cleavages. It i s uniaxial negative with omega = 1.532(1) and epsilon = 1.503(1) (Mont Sain t-Hilaire), omega = 1.5265(5) and epsilon = 1.5020(5) (Nanna pegmatite) and is non-pleochroic. D-meas. 2.15(1) and D-calc. 2.17(1) g/cm(3). The minera l is hexagonal, P6(3) with a 10.828(3), c 10.516(4) Angstrom, V = 1067.8(5) Angstrom (3) (Mont Saint-Hilaire), a 10.864(4), c 10.539(4) Angstrom, V = 1077.2(5) Angstrom (3) (Nanna pegmatite) with Z = 2. The strongest lines on the X-ray powder diffraction pattern [d in Angstrom (I)(hkl)] are: 9.38(10 0)(100), 4.59(70)(102), 3.77(50)(112), 3.36(55)(211), 2.491(80)(213), 2.143 (65)(223,402). (Mont Saint-Hilaire). Electron microprobe analysis (average of three) for micheelsenite from Mont Saint-Hilaire gave: CaO 16.90, Al2O3 6.70, Y2O3 18.07, Gd2O3 0.84, DY2O3 2.65, Ho2O3 0.51, Er2O3 1.88, SiO2 0.07 , P2O5 7.80, SO3 0.53, CO2 (8.38), H2O (43.01), total 107.34 wt.%. The idea l formula is (Ca,Y)(3)Al(PO3OH,CO3)(CO3)(OH)(6) . 12H(2)O based on results from the crystal structure analysis and its relationship with ettringite. T he IR spectrum includes the following bands (cm(-1)): 3240, 1666, 1402, 103 0, 924, 579 and 452 cm(-1). It is a late-stage, hydrothermal mineral, likel y developing from highly fractionated Y- and HREE-enriched fluids. It is th e newest member of the ettringite group and the first of this group that do es not contain essential SO4. The mineral is named in honor of Dr. H. I. MI CHEELSEN (1931-), discoverer of the Nanna pegmatite, for his contributions to the mineralogy of alkaline rocks, specifically those from South Greenlan d.