Hundholmenite-(Y) occurs as pale brown, subhedral crystals up to 1 mm across, embedded in REE–bearing fluorite, in a granitic pegmatite at Hundholmen, Tysfjord, Nordland County, north Norway. Two other occurrences in the same area are the granitic pegmatites at Stetind and Lagmannsvik. The simplified formula, obtained from wavelength-dispersive EMP analyses and boron determination by ICP-AES, is (Y,REE,Ca,Na)15(Al,Fe3+)CaxAs1–x3+ (Si,As5+)Si6B3(O,F)48 (x = 0.78). The mineral is trigonal, R3m, with a = 10.675(6), c = 27.02(2) Å , V = 2667(5) Å 3, Z = 3. The crystal structure was refined to R1 = 0.037 for 1720 observed reflections. Hundholmenite-(Y) is isostructural with okanoganite-(Y) and vicanite-(Ce), and the differences in site populations are discussed. The strongest seven reflections of the X-ray powder-diffraction pattern [dobs in Å , (I) (hkl)] are: 4.38 (33) (202), 3.114 (43) (214), 2.972 (100) (027), 2.947 (76) (125), 2.924 (66) (303, 033), 2.681 (36) (220) and 1.978 (37) (235). The mineral is optically uniaxial (–) with o 1.7578(5) and e 1.7487(5). The Mohs hardness is ~5–6; Dcalc = 5.206(9) g/cm3.
Nabesite is found in complex tugtupite-bearing albitites on the Kvanefjeld Plateau, in the northwesternmost part of the Ilímaussaq alkaline complex, South Greenland. It occurs in cavities, covered with albite crystals, in association with gmelinite, neptunite, analcime, gonnardite, lovdarite, trona(?) and opal(?). Nabesite forms aggregates of thin platy crystals, in parallel or subparallel orientation, the individual crystals show the pinacoids {100}, {010}, {001}, and {111} and {111}, both sphenoids, and range in size from 0.05 ϫ 0.5 ϫ 0.5 to 0.2 ϫ 5 ϫ 5 mm. The mineral is colorless and transparent, it has a white streak, and the luster is vitreous. The Mohs hardness is 5-6, it is brittle and shows good cleavage on {110} and {001}, and the fracture is uneven. Nabesite is biaxial negative with n ␣ = 1.499(1), n  = 1.507(1) and n ␥ = 1.511(1), 2V ␣ (measured) 65(5)°, 2V ␣ (calculated) 70°, and has X = a, Y = c and Z = b. D meas = 2.16(2) g/cm 3 , D calc = 2.21 and 2.22 g/cm 3 for V derived from powder and singlecrystal diffraction data, respectively. Data from EMP, SEM-EDS and results of the refinement of the crystal structure gave: Na 2 O 13.8, K 2 O 0.34, BeO 6.26, CaO 0.13, SiO 2 62.4, H 2 O 18.05, total 100.98 wt%. The ideal formula is Na 2 BeSi 4 O 10 •4H 2 O. The strongest lines on the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 6.11(80)(111), 5.97(100)(002), 3.09(70)(310), 3.06(50)(222) and 2.988(60)(311). The unit-cell parameters refined from the powder data are: a 9.722(1), b 10.142(1), c 12.030(1) Å, V 1186.2 Å 3. The structure was determined by single-crystal X-ray diffraction. Nabesite crystallizes in the orthorhombic space-group P2 1 2 1 2 1 , a 9.748(1), b 10.133(1), c 11.954(2) Å, V 1180.8(2) Å 3 , Z = 4. A total of 5704 unique reflections (at 293 K) gave a final R1 factor of 0.028 (wR2 = 0.078). The [SiO 4 ] tetrahedra form sheets consisting of a combination of 4-and 8membered rings, which are interconnected via the [BeO 4 ] tetrahedra (a spiro-5 arrangement as secondary building unit) to form a framework. Channels house octahedrally coordinated sodium atoms and H 2 O molecules with a well-established system of hydrogen bonds. Nabesite is a zeolite with a new type of framework; the framework density is 16.94 T / 1000 Å 3. Relationships to the crystal structure of weinebeneite are evident.
Heulandite-Ba, ideally (Ba,Ca,Sr,K,Na) 5 Al 9 Si 27 O 72 •22H 2 O, is a new zeolite species in the heulandite series, occurring as an accessory mineral in hydrothermal veins of the Kongsberg silver deposit type at the Northern Ravnås prospect, southern Vinoren, 14 km NNW of Kongsberg town, Kongsberg ore district, Flesberg community, Buskerud county, Norway. The mineral has also been found at the Bratteskjerpet mine, Saggrenda near Kongsberg, and in hydrothermal veins in quartzite at Sjoa in Sel community, Oppland county. Heulandite-Ba occurs as well developed, thick tabular, trapezoidal crystals up to 4 mm across, showing the forms {100}, {010}, {001}, 111} and {201}. The mineral is colourless to white, rarely very pale yellowish white or pale beige, with a white streak; transparent to translucent, with a vitreous lustre, pearly on {010}. The mineral has a perfect {010} cleavage; subconchoidal to uneven fracture. It is non-fluorescent in long-or shortwave ultraviolet light. The Mohs' hardness is 3½; D meas = 2.35(1) and D calc = 2.350 g/cm 3. Heulandite-Ba is biaxial positive with n [ = 1.5056(5), n q = 1.5064(5) and n * = 1.5150(5); 2 = 0.0094, n (mean) = 1.5090. 2V * (calc) = 34.1°, 2V * (meas) = 38(1)°; distinct dispersion, r > v; [ , c varying from ≅ 39°to ≅ 51°in obtuse angle q , * = b. An average of 14 electron microprobe analyses on heulandite-Ba from the Northern Ravnås prospect, Kongsberg, gave SiO 2 54.26, Al 2 O 3 15.27, MgO <0.1, CaO 2.65, SrO 1.03, BaO 12.76, Na 2 O 0.34, K 2 O 0.58, H 2 O 13.1 (from TGA), total 99.99, corresponding to (Ba 2.49 Ca 1.41 Sr 0.30 K 0.37 Na 0.33) 7 4.90 Al 8.96 Si 27.00 O 72.00 •21.75H 2 O on the basis of 72 framework oxygen atoms. Chemical zoning is frequent, with transitions to heulandite-Ca and heulandite-Sr. Heulandite-Ba is monoclinic, C2/m, with a = 17.738(3), b = 17.856(2), c = 7.419(1) Å, q = 116.55(2)°, V = 2102.0(7) Å 3 , Z = 1. The strongest five X-ray diffraction lines of the powder pattern [d in Å(I)(hkl)] are: 2.973(100)(151), 3.978(97)(131), 7.941(66)(200), 4.650(66)(-131), 2.807(65)(-621). The crystal structure refinements (R = 3.5 %) of heulandite-Ba were done in space groups C2/m, Cm, C2, and C1, but refinements in space groups with lower symmetry than C2/m did not improve the structural model.
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