George Y. Chao

Shortite in Kimberlite from the Upper Canada Gold Mine, Ontario

Shortite, Na₂Ca₂(CO₃)₃, occurs in the groundmass of micaceous kimberlite dikes from the Upper Canada Gold Mine, Ontario. X-ray, optical, and chemical properties of shortite from the Upper Canada Mine are virtually identical to those of shortite from the Green River Formation, Wyoming. The grains poikilitically enclose phlogopite, magnetite, apatite, and perovskite and are closely associated with calcite, olivine, and aggregates of serpentine in the groundmass of the kimberlite. The groundmass assemblage is interpreted to have precipitated from kimberlite magma at low temperature.

Lukechangite-(Ce), a new rare-earth-fluorocarbonate mineral from Mont Saint-Hilaire, Quebec

Abstract Lukechangite-(Ce), ideally Na3Ce2(CO3)4F, is a new mineral from Mont Saint-Hilaire, Quebec. It occurs as tabular, short prismatic, and barrel-shaped crystals up to 1 mm. It is colorless to pale beige with a white streak and a vitreous, or somewhat pearly on {0001}, luster. Associated minerals include microcline, analcime, sodalite, aegirine, serandite, eudialyte, catapleiite, fluorite, petersenite-(Ce), siderite, astrophyllite, and albite. Lukechangite-( Ce) is soft, Mohs hardness ≈ 4½, brittle, with an uneven to conchoidal fracture, and with perfect {0001} cleavage. Lukechangite-(Ce) is uniaxial negative, ω = 1.728(3) and ε = 1.542(1). It is hexagonal, space group P63/mmc, a = 5.068(1), c = 22.87(5) Å , V = 509(1) Å3, and Z = 2. The strongest X-ray powder diffraction lines [d (Å), I, hkl] are: 5.71(50)(004), 4.31(100)(101), 3.804(50)(006), 3.169(70)(105), 2.877(60)(106), 2.534(70)(110), 2.192(90B)(109,200,201), 1.978(70)(205), and 1.658(50)(209,210,211). An average of the electron-microprobe analyses gave Na2O 14.94, CaO 0.10, SrO 0.12, La2O3 16.36, Ce2O3 29.48, Pr2O3 1.95, Nd2O3 5.88, F 3.58, CO2 (28.40), and O ≡ F - 1.51, total 99.30 wt%. CO2 was calculated by stoichiometry from the results of the crystalstructure analysis. Dcalc is 4.02 g/cm3. The atomic arrangement of lukechangite-(Ce) has been refined to R = 3.4%. The structure is layered parallel to (001), with CO3 groups oriented parallel to the layering forming thick slabs incorporating either Ce or Na cations and a separate Na-F layer. The structure of lukechangite-(Ce) resembles that of huanghoite- (Ce) and baiyuneboite-(Ce) and is isostructural with synthetic Na3La2(CO3)4F.

Reederite-(Y), a new sodium rare-earth carbonate mineral with a unique fluorosulfate anion

Abstract Reederite-(Y), ideally, (Na,Mn,Fe)15(Y,REE)2(CO3)(SO3F)Cl, is a new mineral from Mont-Saint-Hilaire, Quebec. It occurs as blocky, yellow to orange-brown grains up to 2 mm. Associated minerals include trona, shortite, petersenite-(Ce), catapleiite, minor analcime, and manganotychite. The mineral has a vitreous luster and white streak. It is soft (Mohs hardness 3-3.5) and brittle, with a conchoidal fracture and perfect {001} cleavage. Reederite-(Y) is uniaxial negative, ω = 1.548(1) and ε = 1.537(1). It is hexagonal, space group P6̅, a = 8.773(1), c = 10.746(2) Å, and Z = 1. The strongest X-ray powder diffraction lines are [d (Å), I, (hkl)] 2.532, 100, (212); 4.39, 80 (102); 2.774, 80, (113); 2.240, 80, (213); 6.20,40, (101); 1.657,40 (116,314,322,410); and 2.067,30, (105,303). The infrared spectrum is given. An electron microprobe analysis gave Na2O 34.04, CaO 0.70, MnO 1.23, Al2O3 1.31, Y2O3 10.24, La2O3 1.39, Ce2O3 3.54, Nd2O3 1.99, Er2O3 1.19, DY2O3 1.39 (plus minor amounts of Fe, Pr, Sm, Gd, and Yb oxides), SO3 5.07, CO2 (calc) 31.91, F 1.86, and Cl 2.05, -O ≡ F + Cl 1.24, total 99.14 wt%. Dmeas= 2.91 g/cm3, Dcalc= 2.85 g/cm3. The structure has been refined to R = 3.2%. The carbonate layers are thick slabs accommodating (CO3)2- groups oriented perpendicular to the {001} layering, the large cation polyhedra, and the Cl- and (SO3F)- anions. The Na atoms adopt a variety of distinct coordinations. This is the first reported natural occurrence of a fluorosulfate anion.