Alf Olav Larsen

Grenmarite, a new member of the götzenite-seidozerite-rosenbuschite group from the Langesundsfjord district, Norway: definition and crystal structure

Grenmarite, a new mineral of the gotzenite-seidozerite-rosenbuschite group, was found in a syenite pegmatite at the eastern side of the island Vesle Aroya in the Langesundsfjord district, Norway. Grenmarite, ideally (Zr,Mn) 2 (Zr,Ti)(Mn,Na) (Na,Ca) 4 (Si 2 O 7 ) 2 (O,F) 4 , is the Zr-analogue of seidozerite. It is monoclinic with space group P 2/ c , Z = 2, a = 5.608(1), b = 7.139(1), c = 18.575(5) A, β = 102.60(2)° and V = 725.72(3) A 3 . It occurs as yellowish brown, semi-parallel aggregates of elongated, flattened crystals up to 1 cm in length. The mineral is translucent, with vitreous lustre, good {001} cleavage and uneven fracture. Mohs9 hardness is 41/2; the measured density is 3.49(1) g/cm 3 . The strongest five X-ray diffraction lines of the powder pattern [ d in A (1)] are: 2.898(100), 3.027(68), 2.613(26), 2.459(24), 1.853(24). An average of fifteen electron microprobe analyses of grenmarite gave SiO 2 29.85, TiO 2 4.51, CaO 1.84, MnO 8.25, FeO 2.01, Na 2 O 15.43, Y 2 O 3 0.22, Ce 2 O 3 0.01, ZrO 2 31.63, Nb 2 O 5 0.06, F 5.24, O ≡ F 2.21, total 96.84 wt.%. The empirical formula, based on 4 Si atoms, is (Zr 1.52 Mn 0.46 Y 0.02 ) Σ2.00 (Zr 0.55 Ti 0.45 ) Σ1.00 (Mn 0.48 Na 0.29 Fe 0.23 ) Σ1.00 (Na 3.72 Ca 0.26 ) Σ3.98 Si 4 O 15.40 F 2.22 . Grenmarite is isostructural with seidozerite: its structure can be described as built up with three distinct modules connected through corner-sharing: an “octahedral” layer, an “octahedral” ribbon, and disilicate groups. The crystal structure has been refined to a final R of 0.043. The crystal chemical formula resulting from the structural refinement is: (Zr 1.76 Mn 0.24 ) Σ2.00 (Zr 0.54 Ti 0.46 ) Σ1.00 (Mn 0.76 Na 0.24 ) Σ1.00 (Na 3.32 Ca 0.38 Mn 0.30 ) Σ4.00 (Si 2 O 7 ) 2 O 1.96 F 2.04 .

Petrology of nepheline syenite pegmatites in the Oslo Rift, Norway: Zr and Ti mineral assemblages in miaskitic and agpaitic pegmatites in the Larvik Plutonic Complex

Abstract Agpaitic nepheline syenites have complex, Na-Ca-Zr-Ti minerals as the main hosts for zirconium and titanium, rather than zircon and titanite, which are characteristic for miaskitic rocks. The transition from a miaskitic to an agpaitic crystallization regime in silica-undersaturated magma has traditionally been related to increasing peralkalinity of the magma, but halogen and water contents are also important parameters. The Larvik Plutonic Complex (LPC) in the Permian Oslo Rift, Norway consists of intrusions of hypersolvus monzonite (larvikite), nepheline monzonite (lardalite) and nepheline syenite. Pegmatites ranging in composition from miaskitic syenite with or without nepheline to mildly agpaitic nepheline syenite are the latest products of magmatic differentiation in the complex. The pegmatites can be grouped in (at least) four distinct suites from their magmatic Ti and Zr silicate mineral assemblages. Semiquantitative petrogenetic grids for pegmatites in log aNa2SiO5 - log aH2O - log aHF space can be constructed using information on the composition and distribution of minerals in the pegmatites, including the Zr-rich minerals zircon, parakeldyshite, eudialyte, låvenite, wöhlerite, rosenbuschite, hiortdahlite and catapleiite, and the Ti-dominated minerals aenigmatite, zirconolite (polymignite), astrophyllite, lorenzenite, titanite, mosandrite and rinkite. The chemographic analysis indicates that although increasing peralkalinity of the residual magma (given by the activity of the Na2Si2O5 or Nds component) is an important driving force for the miaskitic to agpaitic transition, water, fluoride (HF) and chloride (HCl) activity controls the actual mineral assemblages forming during crystallization of the residual magmas. The most distinctive mineral in the miaskitic pegmatites is zirconolite. At low fluoride activity, parakeldyshite, lorenzenite and wöhlerite are stable in mildly agpaitic systems. High fluorine (or HF) activity favours minerals such as låvenite, hiortdahlite,rosenbuschite and rinkite, and elevated water activity mosandrite and catapleiite. Astrophyllite and aenigmatite are stable over large ranges of Nds activity, at intermediate and low water activities, respectively.

Heulandite-Ba, a new zeolite species from Norway

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 RavnAs 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 short-wave ultraviolet light. The Mohs9 hardness is 3½; D meas = 2.35(1) and D calc = 2.350 g/cm 3 . Heulandite-Ba is biaxial positive with n α = 1.5056(5), n β = 1.5064(5) and n γ = 1.5150(5); Δ = 0.0094, n (mean) = 1.5090. 2V γ (calc) = 34.1°, 2V γ (meas) = 38(1)°; distinct dispersion, r > v; α Λ c varying from ≅ 39° to ≅ 51° in obtuse angle β, γ = b. An average of 14 electron microprobe analyses on heulandite-Ba from the Northern RavnAs prospect, Kongsberg, gave SiO 2 54.26, Al 2 O 3 15.27, MgO 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 ) Σ4.90 Al 8.96 Si 27.00 O 72.00 ·21.75H 2 Oon the basis of 72 framework oxygen atoms. Chemical zoning is frequent, with transitions to heulandite-Ca and heulandite-Sr. Heulandite-Ba is monoclinic, C 2/ m , with a = 17.738(3), b = 17.856(2), c = 7.419(1) A, β = 116.55(2)°, V = 2102.0(7) A 3 , Z = 1. The strongest five X-ray diffraction lines of the powder pattern [ d in A( 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 C 2/ m, Cm, C 2, and C 1, but refinements in space groups with lower symmetry than C 2/ m did not improve the structural model.

Peterandresenite, Mn4Nb6O19·14H2O, a new mineral containing the Lindqvist ion from a syenite pegmatite of the Larvik Plutonic Complex, southern Norway

Peterandresenite (IMA2012-084), ideally Mn4Nb6O19·14H2O, is the first naturally occurring hexaniobate. It was found at the AS Granit larvikite quarry in Tvedalen, Larvik, Vestfold, Norway, by private collector Peter Andresen, after whom the mineral is named. The mineral was found on fracture surfaces and in tiny vugs in the centre of a miaskitic pegmatite dike. It occurs as equidimensional, transparent to translucent orange crystals up to 1 mm with a pale orange streak and a vitreous to resinous lustre. The Mohs hardness is 2–2.5 and the mineral is brittle with uneven fracture and no cleavage. D (calc.) = 3.05 g/cm3 and D (meas.) = 3.10(1) g/cm3. Peterandresenite is biaxial (−) and the refractive indices (white light) are: α = 1.760(5), β = 1.795(5) and γ = 1.800(5); 2V (meas.) = 43(2)° and 2V (calc.) = 40.7°. The mineral exhibits strong dispersion (r > v) and is pleochroic with X (colourless) < Z (pale orange) ≪ Y(medium orange). The optical orientation is: X ≈ c,y ≈ a*,Z = b. The empirical formula based on electron microprobe analyses is (Mn3.92Ca0.05Na0.03)Σ4.00(Nb5.71Mn.13Fe.12Si0.03)Σ5.99O18.57·14H2O. The five strongest reflections in the X-ray diffraction pattern [ d obs. in A ( I ) ( hkl )] are: 9.8977 (82) (001), 7.7104 (42) (110), 7.4689 (39) (20–1), 7.1026 (63) (11–1) and 2.9260 (100) (42–2). The mineral is monoclinic, C 2/ m , with a = 15.329(1), b = 9.4121(5), c = 11.2832(9) A, β = 118.650(4)°, V = 1428.6(2) A3 and Z = 2. Peterandresenite has a novel structure consisting of six edge-sharing Nb-octahedra forming a super octahedron known as a Lindqvist ion. One Mn2+ octahedron interconnects three Lindqvist ions to form a two-dimensional layer perpendicular to the c -axis. A second Mn2+ octahedron bridging with the Lindqvist ion protrudes into the adjacent layer along the c -axis and creates a three-dimensional structure via hydrogen bonds.